Everything USB reports some people are selling them on eBay:
Since not everyone who loves zombie thrashing on the XBox needs a flash drive, you can pick them up on eBay if you hunt for them. Get one for your Valentine or your Alice. We spotted this one for $22 today and hopefully more people will be willing to part with them if you don't want to shell out the nearly $100 for the limited edition game. Remember, shop smart, shop S-Mart.