Now this music of folk genre you can hear, besides the film, of course, only in the Library of Congress of USA. There are laconic note about it there: written in July 1941, executed by Seabell Kennedy, in the state of Alabama. In the film, you can hear it for a few dozen seconds, the rest will be available only by special search on the Internet or if purchased on Amazon.
Reference:Seabell Kennedy Music on TuneFind
You Ain't Got But One Life To Live lyrics - Seabell Kennedy