Erik,
I knew I had read at one point a list of foreign cars on the RGS. I went back through my library and found the list on pages 356-358 of
The RGS Story by Dell A. McCoy, Russ Collman, James L. Ehernberger and Gabriel Bradford. The list covers Silverton, Gladstone & Northerly, Silverton Railroad, Silverton Northern, Colorado & Southern, and Florence & Cripple Creek cars that ran on the RGS. The list is actually quite extensive and covers multiple years. The list is broken down to date, car and conductor on the RGS train.
Daniel