Verizonwireless.com had one a couple months ago when I got it. I have to say, the extended battery is a lot larger in physical size, but not really so much in terms of capacity.
I got the battery "new" from ebay from a top rated seller (new battery for $2
and the door for I believe 3.00 from verizonwireless.com. The verizon website unfortunately just ran out of the extended batteries at the time, and hasn't restocked them since. Maybe my battery capacity problems are due to the fact that the battery is not actually new.