Most GameStops don't even get spare stock in. I think ToysRUs or Target might, but if you're trying to get it from GameStop, you need the order.
However, I'd suggest talking to the employees. That's how the Majora 3DS fell into my lap - the guy asked if I needed a console, and I joked that unless he had the Zelda one, I was ok. Turns out that they'd just reopened preorders temporarily, but didn't announce it. I make it a point to just talk to them and see if I can get lucky for Robin.
Considering how they sell, there's usually one or two that are available everywhere. I expect Wario may be available after release, and Ness, Pac-Man, and Charizard were the last ones to sell out a few days ago. Thetwo Fire Emblem characters are going to be pretty impossible to get. I'm waiting until they release, since then Japan and Europe will get their overstock, and then I can usually find them for decent prices on eBay. Don't bother now, though - they're taking advantage of people who can't wait.