A Japanese instrument retailer in western Japan This shop also supplies written music, tapes, picks and other accessories, as well as a number of items unrelated to music, such as fans and other souvenirs. I don't know how efficiently they handle requests in English, but there's no harm in sending them an email (link on homepage).
Other information about Japanese music and culture (in English)
The Resource Center for Japanese Music
This site looks anything but cool, but it has biographical information on contemporary Japanese composers, and
details on various compositions.
Zipangu:
Assorted information on Japanese music,
including a link to info on Gagaku (Japanese court music)
and a link to the Hogaku Journal, the leading Japanese music specialist journal