I don't, unfortunately. I'm definitely not a materials expert (but thanks for the confidence).
I have always heard/imagined that the 'shiny' metal on older games was nickel and then eventually stainless (depending on shape). Zinc would be for things that you don't touch (coin mechanism receiver). I don't know if chrome plating was actually used or not, but it would be interchangeable with nickel. If it was cheaper to use chrome (and I imagine it would be), then I definitely think BCB's advice makes sense. The nail polish idea would work well. Enamel paint is what will look best. And it's really easy to do - slather on, wipe off. Nail polish would also work well, again as BCB suggests.
If you intend to do your own plating, I would suggest that the control knobs themselves might not be the place to start. Any flat portion is ok, but the ridged areas will be a nightmare using the plating kits (in my opinion). Also, with those kits, prep to an insane degree - sand the area to be plated until the area is feathered into the remaining plating. Clean it well and then try to plate. The plating can take a few 'coats' to build up to where you want it to be.
Good luck, share the results.