I think a hobby shop is an excellent idea. They could sell buildable models of different parts of the park, in addition to the trains. By the way... they already sell a Disneyland train or three.
There is the standard touristy gold train (which is probably WDW, actually), then there are the monorail sets, and finally, there's the (z?)-scale train that goes with the Olszewski sculptures and is made to run on the track used with the Main Street Station piece.