Just read this on Peter Losin's "Miles Ahead" site:
Several months ago the Louis Armstrong House Museum put a large number of Armstrong's tapes online. One of them includes a jam session featuring Charlie Parker and Big Nick Nicholas. The sound quality is poor, and most of the details of the session are unknown, but it is more "unheard Bird." With help from a lot of people I have tried to make sense of this session here.
I'm trying to register so that I can get to hear it but haven't heard whether or not my request was accepted yet.