There's 3 Pete Seeger Folkstage concerts at the link below & the second one is with Big Bill Broonzy, don't know if this is available anywhere else?
http://blogs.wfmt.com/offmic/2014/01/28/pete-seeger-1919-2014/
http://blogs.wfmt.com/offmic/2014/01/28/pete-seeger-1919-2014/