I found some in at a computer shop that also sold computer parts. It was a cool brand with a guy in dark glasses on the otherwise non-descript brown cardboard box, and some shady kanji in the product name. The storekeeper told me they weren't greatly different from the real thing. And since this is Japan, I would believe him. In a Western country I'd be a little more careful. Myrlyn68 has tested a bunch of these cards, so it might pay to talk to him about the particular brand you are interested in.