I used to have a Tuff Stuff 100 amp stock replacement chrome alternator. It was really nice, the chrome never chipped or discolored. It wasn't cheap though; cost around $200. Got it from Jegs.
they have them on ebay all the time but i dont know about the quality..prolly you get what you pay for.if you find a place that sells them cheap PM me,i am lookin for one too
I have a powermaster 165A alt that originally came with chrome. The finish quality was good. I recently disassembled it and painted it black.
I would think that all the major high power alt manufacturers/rebuilders would have a variety of finishes available.
If nothing else an alt shop can pull it apart for you so you can paint/polish/powdercoat it, then reassemble for you.