Before St. Patty's day, I find raw brisket to be more available and relatively affordable at places like Sam's Club, and I like to buy it and cure my own. After St. Patty's day, on March 18, I used to like to head to grocery stores and buy the leftovers really cheap. Last year when I did that, they were still full price, they said that they weren't going to clear them out, and all the packs I saw had a Sell By in June.
Pastrami is an interesting thing. Going back hundreds of years, it's something that has been made out of pork, mutton, and goose. Really, whatever is cheap. Modern day Jewish/American Pastrami (150-ish years of tradition) is always beef, usually plate (fajita/skirt steak), but some times brisket. It really is the beef equivalent of bacon when done right. Anyway, it is not really a "corned beef" that has been smoked. While they are both cured, they are often different cuts of meat, different seasonings in the cure, pastrami traditionally has a seasoned coting, and a different cooking process, where pastrami is both slow smoked and then steamed. Do a lot of people take store bought corned beef, smoked it, and call it pastrami? Yes. Is that "all pastrami is?" No.