If you want to get translators on board, you should probably try out translator-specific forums. I've found good listings at this Professional Translators
directory. It's not a company, but a list of different firms and freelancers. Maybe you could submit a link as an employer?
I think it's a pretty good idea, too bad Japanese is not my language. In any case, a wide google search should give you a ton of forums and translator resources listings. It's one of the ways I look for jobs, you may find other guys interested in something like this too. You should clearly explain how the BitCoin system works though, most freelancers will probably be a bit suspicious regarding unusual forms of payment.