That's a very complicated process if one was to start with a flat sheet of aluminum or stainless. It's got to be cut out, has a tri-fold, slices cut out, and then bent properly? Sounds more like $500 a set to me if it can be done.
The originals were a plastic extrusion, nipped to allow the corners to fold inward, and plated in some way.
Whoever might have access to inside info to find out who the vendor to GM was that supplied these parts might be able to initiate a search to see if the company is still around.
I have one set of NOS ones as spares for my 76 Eldo and paid a lot for them. A new alternative would be great.