The chord book turns out to be one by Larry Sandberg and is titled Chords and Tunings for Fretted Instruments (ISBN : 0.8256.0198.3 Oak Publications). It fractionally shorter and wider than A4, so isn't a "case" book.
It has a range of different tunings for guitar, mandolin and banjo. There are fewer banjo tunings than I thought, but 8 is not a bad start.
I suspect I bought it from the Music Room in Cleckheaton.