HoneyBadger, you're great !!
I already had seen the page about tibetan myths, but all of this will help me, I think.
In fact, I do know about Hilton's novel, and I planned Shambhala to be Shangri La in MA, after the fall of the Hidden Masters.
I don't know if I'll use all of this, though : I want Shangri La to have a strong tibetan "flavor", but I also want to use legends, rumors and conspiracy theories about Shambhala, Agartha (not Dom3's Agartha with the Pales Ones
), hollow earth and the mysterious group called "Synarchy" that secretly rules the world...
I guess I've read too often Umberto Eco's novel "Foucault's Pendulum"
!!
I will use demons and mountain spirits, and perhaps make lhas spirits of the land.
According Arthur Cotterell's "Illustrated Guide to Mythology" (at least the french version I've got), Tibet was first inhabited by black-skinned demons called "gnod-sbyin", that used bow and arrows and spreaded diseases, and they seems to be very similar to "bTsan".
I don't know if they'll be called gnod-sbyin or bTsan, but you will sure have black-skinned bow-wieldind disease-spreading demons as a national summon
!!