I remember seeing a PBS special, that was aired a number of times during fundraising, at least ten years ago. It was a documentary on Uncle Dave, and featured performers that were influenced by him, as well as his influence on the beginnings of the Grand Ole Opry. I don't recall which PBS station produced it, and have no idea if it is in an archive somewhere, or whether it may be available for purchase or loan...but at least this may be a starting point for you. Best wishes.