[WingsToDiscovery]

I know there's a Fairtex gym in Tokyo, Japan, but I don't know if they do accommodations (you should know Fairtex if you're really into Muay Thai).

I honestly think you should be more open to Thailand. You shouldn't make your decisions on "I hear they've got..." There are millions of Thai who get along every day just fine without being bed ridden. And if anything, you'd probably have an easier time in Thailand with the language than Japan, with all the "farang" and whatnot. You can find camps that have English speaking staff/trainers/etc. as well.