Mp3s of Cal Stewart's Uncle Josh recordings can be found here: http://www.archive.org/details/CalStewart_part1
http://www.archive.org/details/CalStewart_part2
Mp3s of the Avon Comedy Four can be found here:
http://www.archive.org/details/AvonComedyFourwithIrvingKaufman
The official Will Rogers web page is here: