Kid Icarus: Uprising lands with six augmented reality cards, but there'll be more than half a dozen available in the grand scheme of things, as Nintendo of America will host events to make new cards available.
The official Kid Icarus: Uprising site simply says:
Check back on this site soon for info about special Nintendo events where you can trade, share, and obtain new cards.
So there you have it. Check back on this site soon for more information, too.