The same thing we tell everyone. Check the Sunday Early Edition of the newspaper. If Circuit City or Best Buy have ads for the Wii, it means they will have them in stock on Sunday Morning. Just get there early and you're set.
Another option is to buy a bundle from Walmart.com. If you don't want the extras in the bundle, just return them to your local Walmart for a full refund.
Log on to bestbuy.com or circuitcity.com and you can have them email you when they are in stock. I got an email before the store opened and purchased it online and just selected in store pick-up. It only took two days for a local store to email me that they were in stock.