By way of explanation, we tend to think first of John and Alan Lomax when we consider song collectors. There were others who preceded them - in North America these include Harry Odum and Dorothy Scarborough. Scarborough's 1925 On the Trail of Negro Folk Songs includes a song that contains a verse with the familiar, "Let her go, let her go / May God bless her, wherever she may be." Her book is a fascinating document, as she comments on the songs and her relationship to them - and interesting in that many of the "Negro songs" she includes obviously came from the minstrel stage.
And then we have Ralph Peer. Peer was a businessman, with little love for the types of songs he was hunting. Still, he went in search of talent, and was responsible for discovering such luminaries as The Carter Family and Jimmie Rodgers. The records he made with them were profit-seeking ventures, and so we generally don't include them in the canon of discovered folk songs; we don't see them as equally representative of the non-commercial music of the period.
But here - now, this is a different story. When auditioning for Peer, the musicians would bring their own songs - the stuff they were playing and singing at home, or at the village barn dances. Eventually Peer would send A.P. Carter in search of Appalachian folk songs that he could "modify" and thereby declare as original compositions (all the better to copyright, my dear). But our friend, Lonesome Lefty, has made available some of the original 1927 Bristol Session recordings. Here are The Carter Family, Jimmie Rodgers, The Tenneva Ramblers (Rodgers' band - they split up while arguing about auditioning for Peer), Ernest Stoneman and others, some of whom never recorded again. The sound quality is good, and the download includes the record covers and liner notes. A wonderful find - thanks, Lefty! You can download that album here.
(If you are interested in more detail about these sessions, I can recommend "The Bristol Sessions: Writings About the Big Bang of Country Music," published in 2005. Other highly readable resources include Nolan Porterfield's Jimmie Rodgers: The Life and Times of America's Blue Yodeler and Mark Zwonitzer's Will You Miss Me When I'm Gone?: The Carter Family & Their Legacy in American Music.)