D. Scott Chatfield
It appears that most of the large railroads published a "Directory of Industries" circa 1940, and they often included a lot of info about the cities served as well. An absolute gold mine of info.
My undated L&N Directory (but obviously circa 1940) also gives daily output figures for many of the coal mines they served, and also lists many industries that they served through team tracks or through reciprocal switching arrangements.
Ted Schnepf in Chicago-land sells copies of several railroads' directories but I don't think he has the Southern's. I'm going to let him copy my L&N.
Also, the archives has a Xerox copy of the original Norfolk Southern's directory. Hopefully I marked which box it's in ....