I have managed to acquire one of the three cars that came with the S scale American Flyer Frontiersman set. There are three cars that make up this set; a baggage car, a combination baggage/passenger car and a regular passenger car. I would like to acquire a second baggage car to convert into an express/mail car. I'm still trying to get my hands on the combination car as well as two passenger cars if I can swing it. There are more of these on eBay than I expected to find. It looks like any freight cars I want will have to be scratch built though and I'll need to acquire the American Flyer knuckle coupler trucks so that everything works together.
Here are pics of the recent acquisition along with a few Black Scorpion Miniatures for scale.