Looks like people have already mentioned Tama Trading a few times. I had luck with them selling me a case (10 lb) of Rosa Grande Stick a couple of months ago. They said there was a shortage and they charged $8.25/lb which seemed high to me compared to other resources that seemed to price it a little more like $6-7/lb that are located in the northeast US or for wholesale.
If you're looking for a quick fix and need some Rosa Grande Stick for a little more (maybe more like $10-13/lb, but I forget), there's a spot that seems to stock it in Culver City (they also are supplied by Tama Trading, according to Tama). It's called Sorrento Italian Market. They also had some LM mozz loaves that I tried that were good, but I forget the pricing.
Regarding Cheese:
Restaurant Depot is currently wide open to the public and there are so many locations scattered throughout LA county and beyond. User Jsaras advised me that Van Nuys, CA RD carries the Saputo Gold and I've been loving that option lately. I haven't had Grande to bake with in a long time, so I can't really compare it directly, but I'd say they both scratch a similar itch for me when it comes to NY style pies.
Wholesale not open to public:
I'm not really too informed when it comes to these options as I am just "public" and don't have accounts with any wholesalers. That said, I spoke with a helpful rep from Hormel when trying to source Rosa Grande and he pointed me to the following options for those of you who have restaurants: Jacmar, Sysco, Shamrock, PFG & Tama. Apparently Jacmar had been open to the public during early COVID and they have Grande Cheese, too. Bummer that they're no longer open to the public! I missed out.