A tipster just sent in some details on Best Buy's sale of the Xbox 360 Elite. The street date will be April 29, and all stores are mandated to hold all stock until that date. Of course you'll get the one or two who "forget," but that's pretty much when you'll be able to get it.
However, if you're one of owners of the white Xbox 360 who just want some black accessories, those can be sold whenever. So keep checking your local Best Buy, and as soon as they get the black controllers, chargers, and headsets in, you can grab one for yourself.