The article link below from Dick Eastman's Online Genealogy Newsletter (EOGN) reminds me of the brickwall segment of our workshops held every third Wednesday of the month for members and guests of Root Cellar Sacramento Genealogical Society. A reader of the EOGN asked for help in locating an old book after he thought he had exhausted all known sources. Dick tossed the inquiry to his readers and received many comments some of which may be helpful to you.
See the full article:
From the In-box: How to Find an Old Book - Eastman's Online Genealogy Newsletter