I find Whole Packers at Costco and they have both prime and choice. I also find them at Albertson's and Wally World (they will order them in for you). I have a pretty good eye for judging beef. I have done Prime brisket, and can't tell the difference between the hand selected Choice brisket that I do. I have even done a select grade once or twice and they were pretty good. Jobiewan hit the nail on the head with his cooking method. you can use your thermometer right up to the end of the cook. I usually start probing my brisket at 190 degrees IT. I have actually had some that probed as done at that temp. I probe again at 200 degrees IT and pull the ones that are done. I have had one or two that that went to 215 degrees before they probed right. I don't wrap my brisket until it is ready to go in the cooler.