You may have luck talking with your local truck repair shop, particularly if you can give them a sample to work from. I have a local shop that does quite a bit of spring and suspension work and their spring shop can source or fabricate almost any spring from a lightweight utility trailer to truly HD truck springs - old to new. The last job I gave them was overhaul of springs for a WW2 Canadian army trailer (re-bush, replace broken leaves, new clips and center bolts, re-arch), satisfactory result.
