I'd add anything by Beuell Kayzee,

Howard Bursen (on Folk-Lethargy)

Paul Cadwell if you can find him.

Billy Faier and Bascom Lamarr Lunsford.

Coon Creek Girls

Granpa Jones.

And the too humble to mention himself, Art Thieme, who has a style of playing that I find to be a very, dare I say pure, folk style.

Don