As the other posters have said, Wiis in the wild are still a rare sight throughout the U.S. If EB Games is to be believed, the shortages will last at least another four or five months. After that, you should hopefully be able to grab one off the shelves.
Or you could do what some of the others are suggesting, and just wait outside a Best Buy on Sunday. Get there early, though, since they're usually gone less than a half hour later. And make sure you try this weekend, before the Mario Kart and Wii Fit releases, or it's going to be a long summer.