Off the top of my head, in terms of commercial availability I've seen them at:
Beyond: - Safeway (both meat patties, and frozen boxed crumbles) - Del Taco - Carls Jr. - Veggie Grill
Impossible: - Umami Burger - White Castle - Smaller retail locations - pilot w/ Burger King
Beyond also has a lot of products, from sausages, crumbles, and different flavors of meat.
I think Impossible is highly focused on reproducing ground beef.