I work for Gamestop and my manager just got a free one in the mail. In fact ALL GS managers should have received one just like that in the mail for free. Dont know if this helps or not but I doubt its to rare.
Well if it is one per store then its pretty much the same rarity as most not for resale demo carts. If your store had 100 or 200 of them to hand out to promote the game then its a common demo disc. If it was a common demo disc (ie worthless) I was just going to give it to a customer at my store but it sounds like it is worth holding on to.
