I had ox tail soup at a friend's party one time. They are Chinese American. I imagine you can get them in a store that sells ethnic/Chinese food, if you have such a store near you. Here, there is a fairly large Chinese community and my partner is Chinese American. Duck feet and chicken feet are commonly served Dim Sum fares. Actually pretty good: it is the sauce they are cooked in that makes it.
We do have a number of oriental stores here too. I've been to them when looking for ginger stem. I'm not a big Chinese food person. Though since I've been married I eat many things we didn't have growing up, like Mexican and Chinese. I'm not sure what we get in the Chinese place is really authentic Chinese food though is it? Egg Foo Young?