I've seen them from time to time elsewhere in very limited quantities, but they are usually a bad deal. Apple refurbs come with the full factory warranty same as a new Apple. I assume they go through very high quality testing, and are repackaged as if new.
Other refurbs are essentially used computers that some third party has tested in some way, with a very short warranty that has to be handled through them. Often original accessories and CDs are not included.
But if you really want that, you can look at Powermax.com, themacstore.com, and occasionally buy.com.