There's a private group that does that. I believe it costs several thousands of dollars to get their updates with sales numbers. They are the NPD group, however they do not include Wal-Mart stores (just a little FYI).
Wal-Mart doesn't provide any of their numbers to anyone anymore from what I know. I work for a market research company, and a couple of years ago Wal-Mart decided that they weren't going to sell their data anymore. It sure did turn our world upside down.