This post is a hybrid cross between REAL TRAINS and HiRail.
I just finished a project that shows the possibility of producing cars for a road that has little chance of being produced by a major manufacturer.
One of my home roads was a short line, the QA&P, that once thrived when the ICC was in control.
Illustration 1 shows an HO car of a GARX car that actually existed and was leased by the QA&P from General American and Evans Products, and could be found in the consists of the famous trains QLA and QSF. These trains were moved in 1973 (?) from the QA&P to a more direct route from Tulsa, OK thru Enid and Avard, OK. Prior to 1973, it didn't matter which route made the most sense...it all depended upon who made the loudest petitions to the ICC and what the government entity deemed as the winner.
The decals used are HO scale and scanned into MS WORD and doubled in size to make them O scale. The WORD file was then made into a .pdf file to take to the print shop and laser printed onto waterslide laser decal paper. The car was painted an approximate orange to the prototype car with black ends and a silver roof (all done with rattle cans).
This end product might horrify a rivet counter, but I can't get my heart rate down with the end result.
I only post this to show the possibilities of what you an achieve if you can't get cars for your favorite road.
My skills as a modeler are moderate, at best. This car could be better. Yet...
I hope to see other peoples' examples of "dreams come true" on this post. This first attempt has me ready to create a fleet of freelance GARX and QAP mech reefers and plug door boxes.