Many places in Tibet you see yaks grassing along the roads and on mountain sides. They are everywhere, also on the menu. You can get yak soup, yak stew, yak dumplings, etc.
Yak meat is sold in market places and at butchers, where every part of the animal is for sale; head, intestines, organs, you name it. When you see the meat lying or hanging around the streets, you kind of try to supplant that that’s probably also where restaurants get their meat from.