By game stores do you mean Game Stop? Because if so, that's your problem. Go to Best Buy or Wal-Mart.
It's not-so-much shortage, it's they only order 1-2 extra copies because they want you to preorder. The loads of 360 versions you've seen could very well be ones that people have preordered (and I wouldn't put it past the typical Gamestop employee lying to you and telling you that those are for sale).
-edit-
And on the topic of PS3 shortages and Gamestop, when I replaced my old PS3 with a slim last weekend I encountered one of the terrible type of employees! I went to my usual Gamestop where they know not to bother me with preorders and crap to buy the PS3 but they were out. Typically, I would just go to Wal-Mart or Best Buy but I had $100+ in credit so I needed to go to Gamestop.
The only one nearby that had a PS3 was one I had never been to before but was still close. I went to that one, asked for the PS3, he asked me if I wanted games to go with it and I told him no, I'm just replacing my old PS3.
He proceeded to bother me five minutes about not preordering anything else, not buying controllers, not getting any games to go with it. Fuck man, I just want to get my PS3 and get out of there. I obviously already have games for it so leave me the Hell alone.
Needless to say I'm not going back to that Gamestop.
