Hispanic markets are a good source. To prepare it, boil it in a stockpot, then plunge it in cold water and peel off the skin and trim the base of gristle and fat. You can then cut it into thin slices and serve it hot or cold. Different tongues can be used interchangeably in recipes though their cooking times vary according to their size. Tripe is the name given to the stomachs of various animals, but most recipes that call for it intend for you to use beef tripe.
Cows have four stomachs, and the first three yield merchantable tripe.
Honeycomb tripe is meatier and more tender than the other kinds and considered to be the best, but all these kinds of tripe can be used interchangeably in recipes. Tripe is almost always sold bleached and partially cooked. This saves a lot of work, since unprocessed tripe would need to be cooked for many, many hours to make it tender enough to chew.