Here is an idea, I won't do it because I think it is kind of pathetic/dishonest, but if you are really desperate because you just missed getting your Xbox 360 at the store you could try this:
Scenario: Say You just stood in line at 8AM at Target. You were 5th in line, they had 4 consoles. (Even if you weren't there, if you know for sure the store sold some that day you could try this).
1) Get ahold of Target Corporate (or regional, General Manager, Store Manager, etc) later in the day. Tell them "I was in line to get an Xbox 360 this morning at XXX store and I was turned away and told the consoles were gone. 10 minutes later I walked by and heard a kid tell an employee "I am XXXX cousin, I am here to get my Xbox". Tell them the employee came out of the back and rang the kid up (This is really happening out there, so it isn't that far fetched!).
2) Explain that you have been at various Targets when the stores open everyday for over a week trying to get your hands on one of these.
3) Demand/ask that they find you another console as soon as possible since you were treated unfairly as a customer.
Ok, there are holes in this (like if you don't have the employees name, etc), but you never know, you might get that one guy who doesn't want to leave a customer with a bad taste, and he might actually find one for you...
And YES. It has come to this