Yogi Chen lived in Nepal for something like 15 years, being in semi-retreat most of the time, this was in 1960's and early 1970's. During that period he met and taught several persons who later became very influential in modern world buddhism, like Ole Nydahl, Allen Ginsberg, and others... I think Lama Surya Dass is also one of them.
Then in his own words he was invited to the United States by the Dragon King of North America, who appeared to him in his meditation hut in Nepal !!!
I wonder if not any his lectures in States and Canada were filmed or taped ??