Rakuten Global Market has got a free shipping deal going on with some of the stores that sell through it. They'll pay up to 5000 yen of your shipping costs if you spend 10000 yen at one of the stores. The deal is good through 10 AM Japan Time on Friday morning (9 PM Thursday on the East Coast of the US). Items must be shipped by the end of June to get the free shipping, so you may be able to preorder boxes of cards and take advantage of this deal.
I haven't done a thorough look to see what card shops are participating, but I did see that Niki is.