The manual, with the exception of the last couple pages (because of the old license, but also cutting out the shortcuts) is included in the GoG version. Good to have more sources.
BTW, I just went and looked up the Brady Games Strategy guide that is advertised on the last page. Reviews make me think that it's nothing I have missed. At the same time I realized that on Amazon at least, NEW physical copies of the game are selling for about $70! Meanwhile there is currently a sale at GoG: $2.50 for the digital copy.
ETA: While looking around I saw
American Rails, a new game supposedly coming later this year. I don't have high hopes for it (seems to be linked to Steam, releasing on consoles as well), but it's hard to tell too much before gameplay footage becomes available. There are a few screenshots, but I can't accurately determine from these how detailed the economy and game dynamics are. The graphics look good, so I wonder if coding will be efficient enough to allow building a large rail empire?