I've always had good luck at HEB getting what I want in thicker cuts than they put out in the case. Not all HEB's have a butcher shop though. I've also gotten meat at Perry's Meat Market that was wonderful but it's too far for me to drive over there just to get meat. For a prime rib roast, yeah, I'd drive over there.
I'd agree with the HEB rec, specifically the one at Bunker Hill. They can cut it for you.
What about Pete's Fine Meats on Richmond?
To be honest with you, whenever I do a standing rib roast (bone in) I usually just get it at Rice Epicurean. True, it's not prime, but it's not dog food. They usually run specials on Saturdays.