From what I can glean from reading, bluff oysters are similar to native oysters in the UK, both in terms of their rounder shape and more delicate creamy taste. Pacific oysters are the same/similar to rock oysters here.
I just looked, and the oysters harvested on the Texas Gulf coast are called "Eastern Oysters" (Crassostrea Virginica). They are mostly found in the bays from the central Texas coast up and into Louisiana. They are rather large. I don't like oysters raw, so I've mostly had them cooked, usually in the shell.
I can get those live at HEB, although I may need to pr-order them. They aren't always in stock.
CD