A piece of tire tread would probably work to replace it.
That’s funny. Look closely at the existing bumpers and you will see that they have been replaced with tire tread!
My ‘52 3100 came with overload springs and they appear to be factory, listed on page 434 of the 1929-1954 Chevrolet Master Parts and Accessories Catalog under 7.503, Spring Assembly, Rear section. 47-54 Util 6 leaves (Aux Springs) Part 604934.
