Check out Stefan Grossman's Guitar Workshop on the net. Lots of instructional books and DVD's there (and some mammoth video tapes on the Rev.). I'm not sure he has anything that deals with the Piedmont style specifically but I picked up a lot of that stuff from Grossman's Masters of Ragtime Blues Guitar volume which included pieces by Blake, Fuller, McTell and some simpler Rev. Davis stuff along with Broonzy and BL Jefferson. The book Rev. Gary Davis/Blues Guitar includes quite a few numbers that don't require 11 fingers and 2 brains to play, as well.
At Homespun Tapes you also might find some Roy Bookbinder material which deals with Piedmont artists including Pink Anderson. His arrangements are generally pretty easy.vl