After a few emails into the ol' CrackBerry tip line and a couple of phone calls, we've verified that the AT&T BlackBerry Z10 is now available for purchase at select Best Buy locations. While the device isn't set to release on AT&T until Friday, it looks like Best Buy is jumping the gun to get a head start. From the looks of it you won't be able to order online, but you should be able to head to most stores and pick one up. Both the Verizon and T-Mobile models are still listed as coming soon so we'll see if those show up early as well.
Unfortunately it looks like you won't be able to buy the Z10 outright though, so unless you're buying on contract this isn't the option you're looking for :)
*Update* It looks like the stores aren't giving up the Z10's anymore. We've tried numerous others and they are now telling us that they can't sell the devices until Friday.