Check the canned beans -- I've been in supermarkets from Massachusetts
to California and points between both North and South -- no lack of
Black beans. Black beans are also found in the dry bean section and may
be called Turtle Beans. You might also find them in with Mexican food
but check the label for added fat (meat) for flavoring. I've used
Hanover's but got a good buy on Furmano's (also called frijoles negros).