I don't think you'll have a problem finding someone to powder coat them ... but you might want to reconsider the idea.
Powdercoat is impossible to touch up if it chips ... it's impossible to remove ... and, if you get a chip in it, rust will travel endlessly and you won't be able to get to it. If you've ever seen these big work trucks that have bumpers all rotted out (big time), you've seen the results of powdercoated bumpers.
