I remember Ztrack used to have them with their add for a heavy duty flatcar, but I stopped seeing them in the back of the magazine.
The Marklin 12 wheel flat wagon has some underneath it. I have replaced them with MTL archbar trucks to make a very passable British ' rectank' tank carrier wagon used by the british army from 1916 onwards. I use the 6 wheel trucks under the 12 wheel RA22 tenders I put behind my Nickel Plate H6 Mikados. You can pick these wagons up on e-bay quite often. Over here in the U.K I usually pay about £12 for them which is worth it just for the trucks alone.
Marklin's heavy duty flat car has them, been un-ableto get them separately though through walthers. I have seen them used with the Hallmark passenger cars quite abit.
