Sold by Duratrax. I picked mine up off Tower. I looked on their site it seems they aren't available any more. This is the link to part number.
http://www.duratrax.com/discontinued...ion-parts.html
Bunch of info here.
http://www.rcuniverse.com/forum/m_51..._1/key_/tm.htm
Since this thing is discontinued picking up spares for key parts could never hurt. I have a whole extra buggy for spares. I am eventually going to break down and buy the nice machined aluminum carriers, and servo mounts and stuff.
I am pretty sure that ofna diffs will fit and work fine. The Raze shares many parts with other bodies. You just have to do a little searching.