James C. Marsh (the grandson of O.W. Marsh, the last superintendent of the WVM) has done a book on the railroad entitled:
A Pictorial History of the Holly River & Addison RR and West Virginia Midland RR and Webster Springs
It's soft cover and available diirectly from Mr. Marsh himself.
Jim Marsh
10 Rustic Drive
Buckhannon, WV 26201-2448
Check with him on the price, as I am sure it's gone up since I got mine.