Do not know of any one that makes any gears for in the diff cup other then the stock ones. I have not had much problem with the stock ones even with my TZ. The only diff housing I know of sorry to say is made by GPM. Sorry to say I had to get one for my back diff do to the stock plastic one was giving to my flex and eating up my hardened final gears even after shimming when I put my OS 18 TZ in. They sure could have made them a little better but seem to be working. I got mine off ebay. Now Nova makes alloy diff cups.
http://cgi.ebay.com/HPI-Nitro-MT-2-A...qcmdZViewItem\