Good move SF - Myoko has some of the very best back country in all of Japan. Will be easy enough to find gear but you could also contact Bill Ross at Myoko Backcountry Ski School who runs courses and rents gear.
http://www.myokokogen.org/mbss/english/index_e.phpTelemark Ski School and Backcountry Guide Center
218 Shin-Akakura, Myoko-shi, Niigata-ken 949-2102
e-mail:
mbss@myokokogen.orgTel: (0255)87-2392
Let him know you were referred on from here.
Good Luck! ~ MG