There are at least 4 separate villages/groups of people that live in the general area and the Jusenkyö Guide.
Joketsuzoku which Cologne, Shampoo, Mousse, and Shampoo's dad come from.
Musk may live farther away from Jusenkyö but still in the general area.
The often forgotten girls Pink and Link are said to be from a neighboring village called Yakusai. Not the same village as Shampoo.
All four villages/ groups use magic. The Joketsuzoku even have magical toys.
Groups 1-3 practice martial arts. Whether group 4 practices martial arts is unknown besides Pink and Link.
Groups 1,3, and 4 use mind control.
Joketsuzoku have memory manipulating shampoo, remote control pressure points, hypnosis mushrooms, and suggestion incense.
Phoenix use some type of magic eggs.
Yakusai use plants that are able to manipulate people.
Whether the Musk uses mind control is unknown.
While it appears that all four groups use little modern technology, the Joketsuzoku at least are familiar with it and some near modern technology does exist in the area (the guide has a phone and the Joketsuzoku have a newspaper). How much modern technology they have is unknown.
The Joketsuzoku and Yakusai have at least basic trade since that is where Shampoo went to get herbs and ran into Pink and Link the first time and share a newspaper.
The Musk (to the point that Cologne thought them extinct) and the Phoenix (because they look down on humans as being inferior) mostly keep to themselves.
Groups 1,2,3 view the rest of the world as inferior to them, group 4 may or may not.
All four groups have a fairly low population.
Groups 1-3 practice or had in the past practiced some types of Eugenics.
Joketsuzoku outsider marriage laws pretty much define this
Musk used to use Jusenkyö water and animals for this purpose
Phoenix drank from Jusenkyö to alter themselves and use the waters of Jusendo to power up their king Saffron.
Groups 1-3 are ancient races, The Joketsuzoku have been around for a minimum of 3000 years, the Musk 1400 years according to Herb, and Phoenix people at the very least have been around for 4000 years and likely much longer.
Personal theories and things that are inferred.
It is possible that the villages use magic to keep themselves hidden away from the majority of the human population. Doesn't have to be a lot, a compulsion to stay away from the area and mind controlling the few people who ignore the compulsion and do come into the area would be enough; especially since it's a remote area with little reason for most people who didn't know about Jusenkyö or the people who live in the area to go to anyways. As for the government all they would have to do is use some mind control on some of the top officials with the suggestion that there is nothing in the area worth investigating (We see that the Phoenix people if not any of the others do mind control government officials using the magic eggs).
All villages most likely have more magic items and magical items that are more powerful then we are shown in the manga. The most powerful objects would probably never leave the villages and would most likely be limited to a few individuals of the tribe.
Doubt Cologne would leave the village with the most powerful objects or that we saw all the objects she had with her.
Herb didn't see any need to bring any magical objects beside the ladle.
Doubtful Pink and Link would be allowed to take the most powerful objects in the tribe.
Phoenix people may not of had the time to get the objects or more likely didn't see a need for them since Saffron with the object he had should be enough to stop just about anyone
The majority of the Joketsuzoku do not know about Jusenkyö. If they did then Shampoo would have known more about the springs and the people of the village would have probably recognized the Jusenkyö guide and assumed that the panda was a cursed person.
It is inferred that the Phoenix know more about Jusenkyö pools than the other tribes. Kima actually says it and the Phoenix people have been using the springs for thousands of years.
Group 1, 4, the Jusenkyö guide, or another unknown group have an organization known as Jusenkyö commercial goods. That is where the instant cursed water and water proof soap came from. Some of the other magical items may of came from there as well (like the super soba since it also had a bar code like the instant cursed water did). Since most of the Ranma 1/2 world doesn't appear to know about magic this organization most likely has some type of screening process and likely only sells to people who have been touched by magic. Alternately the sale of magical items is generally tightly controlled and is black market merchandise. If I ever get around to actually writing fan fiction that I feel is good enough to post; I plan on Ranma purchasing magical items from this organization.
Very few people have curses/visited Jusenkyö who weren't from the local area probably less than 100 because Taro was able to track down most of them while trying to find Happosai.
The Joketsuzoku are not completely Matriarchal (they are called Aamzons in VIZ translation in the original manga they are called the Joketsuzoku and live in the village of Nyuuchezu - which translates to "Woman Hero Tribe"). We assume they are matriarchal because of the village's name but we have no proof one way or the other (could be Matriarchal, Patriarchal, or Gender neutral ruling party). We also have no proof that males are second class citizens because we aren't shown any males besides Mousse who they don't respect (because of his actions) and Shampoo's dad which the author of the manga didn't feel like giving screen time (and some guys who were in the crowd during the tournament Shampoo was in, We also don't see any other females besides Cologne and Shampoo). If they are Matriarchal, they definitely are not militaristicly so. If they were they would not allow Mousse to have become as powerful a martial artist as he is, teach males any techniques that could in some way make males superior to females and a threat to the ruling body, or want to bring strong males into the tribe (since they could theoretically usurper power). If they were man haters like some fan fiction portray them to be than why do they let Mousse get away with the things he does (Back talking to Cologne or stalking Shampoo)?
While the Joketsuzoku laws appear to be very unforgiving, they are no worse and a lot less weird than laws that exist in some parts of the world now or had in the past:
In 100 A.D., the Teutons, an Germanic tribe, would punish anyone caught as a prostitute by suffocating them in excrement.
The vow of a Roman vestal virgin lasted 30 years. If she engaged in sex before then, she was punished by being buried alive.
Recently there was in Sudai-Arabia a woman was given a punishment of a hundred lashes by whip after being raped. The law she broke was being in a car with mixed company not directly related to her.
Like some places in real life the Chinese government appears to have little to no power over the area.
Possible holes in my theories corrections:
Genma's guidebook - The guidebook doesn't have to have been an official one it could have been made by someone and then given to Genma. Another possibility is that it wasn't a guide book at all. Since it was in Chinese (maybe not even in a common dialect or an ancient one) and Genma doesn't read Chinese. It could of been a guide/map of places to avoid while in China, or a book on magic places similar to books that list haunted houses in real life, or a scam similar to maps to the fountain of youth that just happened to be right.
The guide dressed as a government worker implying that the Chinese government has some people in the area. The guide doesn't have to work for the Chinese government. The Joketsuzoku, Musk, Yakusai, or another unknown party could be the ones who hired him. That might not be a government uniform and if it is it could just be so that people will listen to him and think he is a government official. He may just like wearing the outfit or buys them cheap since Ranma has worn a Maoist uniform in the manga as well. After explaining the curse he might of been told to convince the cursed victim to go to the Joketsuzoku village or another village so that the cursed individuals can be dealt with properly. Also when you look at how nice his house is it is doubtful that he is being paid by the communist Chinese government or that if they are that they are the only ones paying him.