Not sure if you are still in need of information but Ishibashi Music is one of the larger Music supply stores in Japan and might be able to assist you will getting equipment
Ishibashi Music
Shimamura Music is another good store:
Shimamura Music
I'm not too familiar with this website but MusicBizJapan is a website community for musicians in Japan. You might be able to get advice there:
MUSIC BiZ - Japan Music Industry Networking