Like my link says, it's hard to find.
But there is a reference there to a new Cassavettes biography
called "Cassavettes on Cassavettes" which might be of some help.
Also check the torrents. There is active movement to get
documentaries and other content digitally archived. It's likely
only ever beern transferred to vhs and hidden in remainder
shelves of vid stores and possibly library archives.
I just checked my interlibrary loan which goes through
all of Wisconsin. No luck. But torrents may turn up something
if a request is made. It's be an interesting hunt. A good intro
site to torrents and new media is called:
http://www.afterdawn.com