I received a blatant bit of advertising through a forum posting, but as it does seem potentially useful, I am passing it on.
The following books were listed at Ancestral Books
A Collection of Family Records With Biographical Sketches, and Other Memoranda of Various Families and Individuals.. - by Douglas, Charles Henry Providence, RI , 1879
My Father's Family (Douglas) - by Rudder, Edith A.
Salem, IN , 1947
The Douglas Genealogy. The Descendants of John Douglas of Middleborough, Massachusetts, the First of this Branch in America - by Douglas, J. Lufkin Bath, ME , 1890
The Douglas Register: Being a Detailed Record of Births, Marriages and Deaths Together with Other Interesting Notes, - by Douglas, William Richmond, VA , 1928
Drumlanrig Castle and the Douglases: With the Early History and Ancient Remains of Durisdeer - by Ramage, Craufurd Tait Dumfries, Scotland , 1876
A Collection of Family Records of the House of Douglass and Allied Families - by Austin, W. J.
n/a , 1940
Let us know if you have purchased from them, and how you got on.
if anyone has read these books, and has feedback on them, then this too would be welcome.