They had at least 20 of them for each system (360/PS3) at my store and also they had an advertisement on there overhead speakers about it so it should be at all or most stores.
I dunno how much goes a good Skateboard cost you? You could just buy some wheels and attach them too it. It's been done but I'm sure it's got some sturdy parts.
Man, at that price I almost want to bite, remembering all those fun nights back in the day with Tony Hawk Pro Skater 3... But I know, I know, this is nothing like that.