Last week at a local antique store I picked up a copy of issue no. 263 of The Pocket List of Railroad Officials, a book that, among other things, provides a nationwide alphabetical index of more than 20,000 railroad officials (management, NOT rank and file employees -- roughly down to local freight agents, traffic managers, and track superintendents), as of approximately the last week of July 1960.
The book includes a listing of more than 500 advertisers, companies that supplied the railroads, listed alphabetically with mid-level sales officials, such as agents of Caterpillar Tractor Co. in Waco, Joplin, Colusa, Aberdeen, and other locations.
I have not found this 1000-page booklet in libraries or on line. I've listed it at Midwest Roots among my other on-line lookups.
The Pocket List of Railroad Officials no. 263, Third Quarter 1960 (New York: The Railway Equipment and Publication Co., 1960).
Harold Henderson, "1960 railroad resource (new lookup)," Midwestern Microhistory: A Genealogy Blog, posted 17 July 2013 (http://midwesternmicrohistory.blogspot.com : accessed [access date]). [Please feel free to link to the specific post if you prefer.]