Some of the Ranma Super Nintendo and Gameboy games can be downloaded from http://www.furinkan.com/ranma/misc/videogames.html and/or http://ranmavg12.tripod.com/vg.html
The second link has the Ranma RPG translated into English. Personally I find the games to be so so. I like the PC Engine game and the Sega Cd (also known as Mega Drive) more than the Super Nintendo and Gameboy games. My favorite type of game is role playing though and the Ranma RPG really is not all that good. There were a few attempts to make a fan made console type Ranma RPG but they were all dropped years ago.
Faq's for some of the Ranma games can be obtained at Game Faq's.
Also if you download the Japanese version of the Ranma Super Nintendo RPG you can add patches from RPG Classics to translate it into English. They have two patches one Manga and one Anime the differences are slight though.