I doubt that printed transcripts, let alone recordings, of ~99.9% of the broadcasts survive. But the history is well documented...if almost unknown to younger folks. For a start:

https://en.wikipedia.org/wiki/John_R._Brinkley#Brinkley_and_...

https://en.wikipedia.org/wiki/XERA-AM#The_border_blaster

https://en.wikipedia.org/wiki/Brinkley_Act

(There probably are wagonloads of printed works - sales flyers, bottle labels, newspaper ads, etc. - documenting the literal "snake oil". Though you might have to do some digging in newspaper archives, libraries, and museums to find much of it.)