Here are two additional Ringling Bros. and Barnum & Bailey cars I located.
First a "human cannonball" truck flatcar (with customized pressed steel Marx cannon truck that can actually shoot a plastic circus figurine):
Second, the circus manager's/advance man's automobile flatcar (with customized diecast Pride Lines REO automobile):
Both of the above will be running at Trainfest 2017 on the SGMA layout.
Bob Nelson