I've talked with Dan about the frustrations he has had otrying to get a lot of the Japanese vintage footage collectors to trade with him...and there is some really neat older stuff in some of those collections. Part of the problem is likely related to the previous discussions about bootlegging... those guys would be an older crowd, and would be extremely wary of trading the stuff they do have, especially to people outside of whatever trading communities that had to have been built over the decades.
If older folks are that adamant about how evil bootlegging things is, I can see why they would not want to take a chance on being revealed as a bootlegger. It's got to be part of the problem, I think.