there's a few ways that I know of.
you can look up "Japan Bases Used Cars" on facebook, Chris Roberts can help you look for cars at auction, does the paperwork, JCI etc. a lot of people have bought skylines from him
I got my silvia off
www.tradecarview.com but they mostly do export but the seller decided to sell it to me anyways. the seller buy cars from auctions as well, if you cant find a car let me know i can give you his info.
hope that helps