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.
The thing is how long are the lines. Are they still steep as before?
From what I understand, 30 minutes is generally enough, but check with the store. Not all stores release on Sunday morning. You may be able to call Friday or Saturday and ask if they will have wiis available on Sunday morning and how early they need to be. Some stores only get them every other week I think.
Gamestop is probably the worse place to get a wii. You will have a much better chance at wallmart, especially for just random spotting it in the wild in the middle of the week. (Assuming you have a wallmart nearby).
The situation may be different on the East Coast, but here in California the lines haven't shrunk by all that much. I went shopping for one with my friend the day Brawl came out, and despite coming in twenty minutes before the store opened, there were still about two dozen folks milling about, and another fifteen arrived before the place opened. Luckily, Nintendo shipped enough to this store that everyone who wanted one got one, but by the time we actually left the store (we spent some time browsing the aisles first), the Wiis were gone. That's where I got my 30 minute figure from.
Oh, and none of the stores we called ahead of time confirmed their shipment dates. Hopefully, the folks in Deleware are a bit more polite, and actually know what customer service means. In any case, good luck on your search!