Murray wrote: "I have no doubt somebody will write in and say that David Wilcox or one of the Wyndham Hill mob use just some such weird tuning on some obscure piece............. "

Try Davey Graham. From this article:

"Still, despite the rareness and deficiencies of some instruments, performing styles did improve in the Sixties. For guitarists, a quantum leap had been the arrival of Bert Jansch ("the first player who really created, not copied"). Davey Graham represented another departure, introducing DAGDAD tuning. "He did it to play Indian material", remembers Archie, "and it also proved for Scottish songs. Different tunings helped me personally. 'Dropped D' compensated for the weak 'bottom end' of the Kalamazoo. Mind you, DAGDAD confused folk, I'd say it took over a decade to become widely accepted.>

(Maybe it's a typo, but it seems to be a consistent typo. I found another web page on Led Zeppelin, saying as how they'd recorded a Davey Graham song in DAGDAD.)