My local friendly steel fabricators made 6 stainless steel brackets from the mild steel one that I gave them as a pattern but I (and you) only need 4 and so I have two left over which I'm happy to send to the first person who would like them. I'll even throw in 4 stainless flange headed screws to screw into the floor.
If your Excel is like mine then at least one of the original brackets will have rusted through. The end with two holes is riveted to the seat back and the single hole is used to screw the bracket to the floor. They are exact copies of the original brackets but slightly stiffer.
I rounded the edges off the ones I fitted into my car as the edges on these and the original mild steel brackets are quite sharp and easily damage either you or your interior if you're not careful.

Just let me know with a PM and I'll send them out.