If you are looking to buy ski/snowboard gear, clothing or just about anything else associated with the sports, there is an awesome street waiting for you in Tokyo. In the Kanda area, close to Jimbocho or Ogawamachi Stations you can find block after block of snow sports shops.
There is a staggering amount of choice with shop after shop, with floor after floor stocked full of everything your heart could desire. The main street has some of the big names in sports goods retailing and some of the side streets are worth a wander too as there are some good little independent shops tucked away. There are usually some good deals to be had, especially if you are not looking for the latest and greatest, and there is one store that seems to specialize in gear that is several years old and hence much cheaper.
You can rent or buy everything you need once you get to Yuzawa, but if you are thinking about investing in some gear of your own, then this is a great place to look.