No secret here. Jim Carter Truck Parts:). I found them 10 years before I found this truck. Great luck sourcing a few underside panels on Ebay.
I needed some splash guards and inner fender wells. Found them easily on-line.
This 1935 has about a 20 year old restoration. I am tightening up the underside with NOS front end parts, bearings, king pins... But, otherwise just plan to just drive this old GMC.
Aftermarket parts would not benefit me here Rette. The rarity of this old beauty is it has the original drivetrain. Most have become hot rods over the years. So, for me. No Aftermarket. But, yes, kits are available for anything.
All the best