Stefan Grossman has certainly been a prolific producer of books on the guitar styles of the classic bluesmen.E.g., Delta Blues Guitar, Oak, Lib Congress 68-23509
Ragtime Blues Guitarists, Oak, 76-113474
Oak also produced a lot of books by other people, such as:
The Art of Folk-Blues Guitar, Jerry Silverman, 64-18168
Finger Picking Styles for Guitar, Happy Traum, 66-19052
Masters of the Instrumental Blues Guitar, Donald Garwood, 67-14542
Brownie McGhee Blues Guitar, Brownie McGhee/Happy Traum, 77-136356, etc
I think the most important thing is to get recordings of the music you are interested in, because you can't learn the feel from a page of tab.There are probably lots of books around if you look in the big music stores, although folk/blues is not as popular as it was in the 60's and 70's.
Regards
Chris