Last night I found, in my stash of old VHS tapes "Long Time Gone" by CS& N. I watched it and really enjoyed it. They played lots of clips ranging from their Woodstock appearance, to a visit on the Dick Cavett Show with members of The Airplane, and also clips from Buffalo Springfield, The Hollies, and Byrds.
It was so intriguing to watch them harmonize. At points even they were amazed! And their individual personalities clearly displayed.
It was a great video and I hope that it is still in print so that you might be able to see it.