I used these guys.. they did an excellent job.. Quanta Products out east.. https://www.gastanks.com/DRIVESHAFT/products/733/ we added the stripes and inspection marks/detailing and then covered it all in a light coat of clear paint.. that shaft is NOT painted silver.. Now this is strickly a cosmetic restoration.. if your talking about having your driveshaft rebuilt/balanced for function, that's a completely different thing, and any competent driveshaft shop can do that. Just ask around at repair shops in your area to figure out who is the "go to" outfit. JW
I had these guys do one a while ago. They have done a couple Wildcat ones and an aluminum one for my 65 GS. Working on a 68 3-speed one this week https://www.cincinnatidriveline.com/ So the first time I went in the guy recognized the Riv driveshaft with no prompting. Never had to go anywhere else after that.