do you mean a diff unit installed into the pumpkin?
if so, there is only one place i would trust and its the place that Sasha uses and that i’ve used to rebuild two diffs.
BC enterprises in some weird unit at the corner of courteny park and dixie: 905-461-9553 ask for Brian. he is the owner.
He doesnt answer the phone all the time, he isnt always there during business hours and you’ll get the run around for 6-10 days longer than the initial quote… but you’ll get someone who knows what he’s doing, gives you the straight shit advice and is very reasonable if you pay cash 
i waited 4 weeks for my first diff from him… havent had an issue after more than 40,000kms with it, it’s in my Kouki.
i took him a carbonetic for a G35 i got off MPD this summer. It was fuckered when i put it in my car making weird noises so i took it out and took it to Brian. He disco’d it… we played phone tag for 3 days… lol… he told me he had seen the same condition in other 350z / g35 diffs and said instead of getting the parts from nissan for him to rebuild the whole thing that i should just get a new diff and swap the carbonetic into it… saved me $1,000 with that advice alone.
when i got a new diff he swapped them and charged me something stupid like $250 or whatever.
he’s a perfect example of a good dude who’s not easy to deal with and you’re going to put up with it anyways because everyone else is a know-nothing fggt… EVERYONE!