When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
What year is your car? Motor? What gear are you changing from/to?
If you don't get a good recommendation and you have an iron differential ('79 & earlier), there are several good rebuilders to whom you can ship your pumpkin for a quality job.
Between google and a search of this forum, you should have no trouble coming up with a list of names. They may even have one built with the gears you want.