No "official list" but here's my list:
Kydex:
BuyBrown (this is my 1st stop for sheaths, quite honestly). He gets every drop IIRC, so he's a good bet.
Mashed Cat (they do pretty good, but they get the more popular drops. ask before you buy if it's not listed)
AZwelke (might have spelt this wrong). Good reputation, good sheaths. May not have every option.
Leather
Azula gun holsters (that's their nic here too). I've never bought anything from them but they seem to do well here so.....
Pirtle made (again, never done business with them) They have a stellar reputation and their work is always making me want to get one)
There are others, but these would be the makers I'd go to.