Tallow is the best! Tallow is rendered beef fat. It is hard to get a hold any ruminant fats besides beef. Many natural grocery stores have beef tallow, duck fat, lard, chicken fat, etc. but not fats from bison, mutton, elk, goat, etc.
Be careful with frying. The cooked fats can sometimes be difficult to digest and cause trouble for some people.
Also, if you have a problem with fats consider getting your hands on unaged meat. On this same page there is a section dedicated to unaged meat and where to find it.