Wanted: Where / when on earth will I find a NOS Suntour Superbe Pro rear derailleur?!

I'm not diminishing your build by any means, but out of curiosity what will you do with the bike once it's finished - presumably it's unrideable with this level of component searching / NOSing?

Why would it be un-rideable? Not something you'd leave locked with one of those shoe-string cables outside the local chippy certainly. But there's middle ground.