Physical and online fixed price lists

These kinds of sources are physical documents or website offerings maintained or contributed by certificate dealers.

Many dealers, myself included, produced pricelists and catalogs in the days before the internet. They generally offered certificates at fixed prices. Once eBay became a force in the late 1990s, dealers gradually abandoned physical lists in favor of web presences and sales on eBay. Most physical lists were highly ephemeral in nature. Many never numbered less than 200, maybe even less than 100, copies. Acquiring such lists today is almost impossible. A precious few can be acquired through numismatic book dealers or borrowed through the American Numismatic Association library. It is possible some exist at (or may be added to) the Newman Numismatic Portal. 

Most professional dealers maintain websites where collectors can purchase certificates rarely seen on eBay. I do not list websites here because their addresses change frequently. Moreover, every website is only one missed payment from disappearance. However, I maintain a special page listing all the professional dealers I currently know of who have been known to offer certificates from North American railroads.