I've seen a Nickel plated Sherpa before, a long time ago at a trial in Cliffe Marshes In Kent....mid to late 70's.
I remember the particular bike as my friend's father had it done as a favour at a platers down in Dover. Part of a job lot for Marconi's (or Elliotts Aviation as it was?).The guy wanted the frame chromed but the platers talked him out of it saying this could make the frame brittle and suggested Nickel as being better engineering solution.
hmm....I can still smell the platers and the picture the sight of hundreds of ping pong balls floating on top of the tanks....I think we used to go to tarmac hill climb down that way, cars mainly but a few bikes too.
...I'm amazed I remember all that, but I'm shallow and always liked shiny bright things....this is one of my gixers's