The amount of old-time radio recordings online is a bit intimidating. There are thousands of hours of shows that have slipped into the public domain. As I’ve been working on a radio-sitcom section of my book, I’ve often used archive.org for its radio recordings.
Here are a few collections that I’ve used:
The Aldrich Family (97 episodes from 1939-1953)
Fibber McGee and Molly (39 episodes from 1940)
Amos ‘n’ Andy (270 episodes from 1943-1955)
All archive.org files tagged with the “Old Time Radio” subject.