Francine,
A nice though having a model of 2124 and some Reading coaches to go with it. But who would manufacture it? Lionel would not be able to make the coaches and if they did the engine, I would not order it. MTH remains to be seen, though I doubt they would make a railroad specific engine, perhaps the coaches, but they have never done S gauge passenger equipment.
American Models would be my choice for both coaches and engine. They already have a 4-8-4, but it is a major effort to make a new engine shell. If the coaches could be used for other railroads I am sure they would sell well.
So for now, I suggest the AM 4-8-4 mechanism and get Bill Lane and Fred Rouse to bash the shell into a Reading T1. I have plans for 2100 that I would be more than willing to share.
Tom Stoltz
in Maine