Check with your local jeweler. Rhodium plating is very common with jewelry... White gold in particular.
Unfortunately, it won't work, Rhodium Plating will not ahere to Brass, copper, aluminum etc. Brass first needs to be washed in a special acidic bath to remove contaminants then plated with a copper strike, then followed by a layer of gold plating, then by a mil spec rhodium plating. The reason rings can be Rhodium plated, is it is made of gold to begin with.
One could do it as a quick temporary fix, but jewelry rhodium plating is a cosmetic grade, not a mil spec grade (there are only 5 mil spec Rhodium platers in the entire USA, 3 of which don't even take on outside plating jobs) so beware that they aren't the same thing and won't hold up well nor adhere to brass well (and would cost about $25-$200 depending on the thickness).
To the OP, i wish we could do that for you, but it is cost prohibitive to do only a part.
Heres an article on Jewelry grade Rhodium plating: http://www.everything-wedding-rings.com/rhodium-plating.html
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