I don't think you'd be able to just get the spokes powder coated without doing the rim aswel.
One Lordz member (not around so much these days) had a ropey set of 14x7 standards powder coated in white and they looked pretty good.
American wires (made in China) are only single chrome plated so they usually start to rust whilst your still having the tyres fitted

I'd spray the spokes silver to cover the rust and get another set for best. (actually I'm too mean to buy another set, I'd just paint em and roll em)
