I work as a research librarian, specializing in part in government publications. Recently, I checked the Government Printing Office’s catalog to see what they may have published on the resonator guitar. I came up with this tiny gem, a one page, typewritten, 1978 guide to books that teach the dobro:

Johnston, Katherine W. 1978. Dobro Instruction Books: A Bibliography. Washington, DC.: Library of Congress, Archive of Folk Song, 1p. SuDoc number LC 1.12/2:D 65.
Thanks to the govdocs librarians at Duke who cared for this item, and for Duke’s interlibrary loan librarians, who scanned and sent it to the interlibrary loan folks at Harvard, who sent it to me.
The bibliography is a short list: books by Mike Auldridge, Bill Cunningham, Ken Eidson & Tom Swatzell, Beverly King, Stacey Phillips, and Keith Tyler. The two earliest books (Cunningham and Tyler) were published in 1971. If, as I understand, Oahu made money selling instructional materials for their Hawaiian lap-style guitars in mid-century, does that suggest that other publishers might have put out material on resonated country or bluegrass lap-style as well, books or pamphlets that didn’t make it into this bibliography?
And does anyone know of the author, Ms. Johnston? A few more titles that she wrote for the Archive of Folk Song at the Library of Congress suggest that she was an ethnomusicologist or music librarian. The byline on the bibliography itself implies that she worked for the Archive and was based at the University of Maryland.
[For more on the resonator guitar, follow me as @DobroSwamp on Twitter.]