Good luck finding anything!

One place you may turn (and I'm sure you've probably thought of this already, but in the off chance you haven't) is archive.org

https://archive.org/details/cloggers-blue-ridge-mountain-dancers-newport-folk-festival-clip-1960s

https://archive.org/details/festival-1967

https://archive.org/details/RainbowQuest26 (brief clip about 40 min in)

Possibly more to be found, but there's a start