Rhino Records has a limited reissue of A Child's Garden of Grass,
which has Peter Bergman (and maybe other members of Firesign
Theatre, but that's not entirely clear):
http://www.firesigntheatrelegacy.com/albums/index6.html

A new NPR segment from Firesign Theatre will be on All Things
Considered for the 4th of July:
http://www.firesigntheatrelegacy.com/npr