Joe,
I have just started reading Lomax's "The Land Where the Blue Began" (After twenty thousand recommendations on the Mudcat). As I read what Lomax did, it sounds like Sandy has the right idea. You have to ask who knows the old songs.
Of course, one of the things you might look for are little pockets of the country where life has not changed so much. And of course, you should be looking for the older generations.
Good luck.
Roger in Baltimore