The Prelinger Archives preserve history via films for future reference. You’ll find old commercials, banned material, old home videos, public service announcements, old news reels, educational material, all sorts of stuff…and it’s all royalty free.
"Rick Prelinger and The Internet Archive hereby offer public domain films from Prelinger Archives to all for free downloading and reuse.
You are warmly encouraged to download, use and reproduce these films in whole or in part, in any medium or market throughout the world. You are also warmly encouraged to share, exchange, redistribute, transfer and copy these films, and especially encouraged to do so for free."
I use a lot of material from there but sometime it can be difficult to find something specific. There is a lot of complete episode or full 2 hours radio show and such in there and to get something out of it, you need to listen to the whole thing.
I highly suggest anyone looking for content to spend 2-3 days downloading and listening to random show from there and just grab and cut what you could use.
It also really open your eyes on other era of broadcasting and generic population ideas which to me, was an eye opener.