Walmart gets deliveries of Wii consoles every Sunday at 12am. I went in around 1pm a few weeks ago and there were plenty still available. No Wii fit though.
Go to Gamestop. Everyone goes to the big box retailers, so they constantly run short, while not thinking about specialty stores. I went and bought a Wii about 3 months ago at Gamestop, walked right in and got one no problem. They had several more in the back, the guy working there said they never have a shortage anymore.