KJW are made of pot metal. There can be many different types of metal. I'm not sure you actually could plate it.
Your best bet would be as Donster suggested - get it down to bare metal, polish it as much as possible, then spray on a clear coat to seal the finish. Even then though, I don't think you'd get a very chrome-like finish poslishing pot metal.
As for a chrome slide - replacement parts for KJW are pretty rare. I hear that the Marui slides are compatible with it, but that would leave the lower frame which could never match it.
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