I would advise seasoning with coarse black pepper and kosher salt. Spritz with water and apple cider vinegar. I like my beef ribs smoked with applewood.
As for sourcing, Restaurant Depot if you know a person who works at a restaurant. Costco had prime short ribs at Tustin but it was a meat roadshow and I doubt they are still there. I know Butchery has them, not sure I would use a high quality meat for something like beef ribs. I go to SuperKing, they have choice and are same sourcing as Costco. Check their ad, some locations have them on sale for < $4 per lb.
Sam’s Club sells choice angus shorts for $5 per lb. You can ask them for uncut ones.
You can always go to Korean market like H Mart and ask for uncut ones from the back. H Mart has CAB Choice ones and I would say they are worth the price.
I usually just get mine at SuperKing because I can get two “racks” for < $25. I don’t think Prime is worth it, beef ribs are fatty enough. Choice is fatty enough and IMO renders much better and still plenty of fat.