I think one thing that isn't being considered here is that aftermarket companies were already making replacement non-OE fenders for the S13 much like they do for just about every other car on the road. The only problem is that these cars are at best 26 years old now- so most of them are now discontinued.
Here's one result produced from a quick Google search:
https://www.nationalautobody.com/cat...7oiag302m2ovc4
And another from eBay:
http://preview.tinyurl.com/y2tvm5lb
So the whole argument of "a company would NEVER be stupid enough to produce a replacement metal fender for the S13" is kind of invalid since it has already been done by multiple companies. Maybe the approach that would make the most sense would be reaching out to one of those companies to see how many orders they would need to start reproduction. I realize it's unlikely, but it wouldn't be a bad place to start if someone really wants to make this happen.
Obviously this does not include JDM S13 Silvia fenders, but you get the idea. I don't know if something similar ever existed in Japan or not. I just bought a replacement aftermarket metal fender for my Pontiac Vibe (lol) for $72 shipped on eBay a couple weeks back and it fit like a glove. How they can even produce and ship something like that for so cheap is beyond me.
Again, slightly off the rails since this refers to USDM metal fenders and not JDM Silvia fenders. No idea how aftermarket replacement parts like this work in Japan or if that is even a thing there.