There's a company, Model RR Warehouse, that offers cars sides, roofs, underbodies for the Cincinnatian cars. In HO.
http://www.prototypespecificpr....com/passenger-cars/ (scroll way down towards the bottom of the page).
The company says it will run items in other scales if a sufficient (several dozen,maybe) number of firm reservations are received.
Are there any out there in 2-rail, or 3RS, land interested in such a product? Or is the community firmly wedded to R-T-R?