The best area to buy snowboard gear is in the Kanda district, and especially a small discount shop called London Sports (sign in Japanese ロンドンスポーツ and just looks like a junk shop from outside, but wander inside to the back to see discounted equipment). http://www.nisekoz.com/tokyoshops.html You won't get a tax refund, but you'll save more shopping there. After my first purchase they gave me a coupon for 10% off my next purchase, so you might want to just buy something cheap the first time, and then use the coupon for something more expensive. There are lots of other bigger stores around so there is plenty of competition.