I had Tibetan Butter Tea at Makye Ame (Beijing), and did not like it.
Yak butter tea tastes like drinking butter...thick butter flavor...and
that's it...*shudder* I couldn't finish but half a cup, let alone the
whole pot! I do recommend Yak as a delicious meat, though!

If you still wanna give it a try, I can you that tou tea is just
toucha, which is shaped pu-erh, and available all over. Also, the "bao
yan" ("holy flame") brick series produced by Xiaguan tea factory is one
of the most popular bricks amongst Tibetans. You can get it many places
online. I'm unsure if the green/raw or black/cooked version is drunk
more often, though, and I'm not sure which kind was in the Tibetan tea
I had (because it tasted so much like butter and so little like
anything else!).

Darnit. Right now I really could go for some mutton ribs or
stone-cooked yak!