This is one of the auction sites, and there are others: http://auctions.yahoo.co.jp/
You will need a bit of Japanese to be able to search some of the items because some listings are only in Japanese.

Say, for example this very rare MK Magic 40:
http://page6.auctions.yahoo.co.jp/jp/auction/f123022362

There are then proxy services like Buyee that help bid, warehouse, repackage and ship to you. There are efforts and costs involved with each step and it isn't a completely painless process, but it can be done if you have some experience. A lot of the sellers in Asia use auction sites as a listing for their products, and request you to contact them before bidding. Sometimes the seller doesn't want to ship, or don't want to work with proxies, etc...

Now that this goes on the net, it'll be interesting to see how the bidding goes!