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Powder coating would be the ideal, and I suspect is how they do the factory finish on some metal bindings. Bear in mind that it adds a thin layer to the object so things with very tight tolerances might not fit well any more and you better be damn sure you mask off any threads. It's also surprisingly affordable, the prep work has to be damn good though.
If I was going to do it I would completely disassemble the binding then get them sand-blasted or acid dipped, whichever was appropriate, to completely remove all the old finish, then get them powdercoated.