Usually I order them from amiami.com or sometimes Hobbylinkjapan. Sometimes you can find them on amazon, but they're usually marked up quite a bit. The problem is that they are only made for a limited run, so you usually need to pre-order them to make sure you get them for a reasonable price. (I check amiami every morning to see what will be released.) Sometimes I get them on ebay too, but the problem with that is you might get a bootleg or the prices are usually really high.