If you make it up to Hokkaido, I live up here and could show you some spots.
Close to Tokyo though, you've got plenty of riding. Closest decent place to Tokyo is probably Naeba in Niigata. Thats only a couple of hours on the Shinkansen. Or you can head up to Nagano area, and hit Hakuba or the countless other ski areas around there. Public transport is really efficient, if you want any tips, just give me a shout.