I don't think they were available as a postwar part either.
When I am working on those collector trucks, I cut the rivet that holds everything together (it's visible on the bottom of the truck), clean up all the parts, and reassemble using rivets from the local hardware store. They are a tad short, but there does not seem to be any ill effects.
Replacement rollers are available.
I have not found replacement pressure springs (goes on the assembly rivet).