I don't know if you've found any leads yet but I highly recommend the book "Maine's Visible Black History," by H.H. Price and Gerald E. Talbot. They've got a pretty substantial section on Malaga Island and there are some references to the Darling family according to the index. Also, Dr. Kate McMahon who has done extensive research on the Peters family of Warren, Maine, has also done some work on the archaeology of Malaga Island. An article she wrote can be found here http://liminalities.net/15-2/slavery.pdf
I hope this helps!