Ran across this website when searching locally for (TN) platers - searchable by state and industry type, I think there are 3189 plating companies listed here, along with companiy profiles and capabilities.
Here in TN, I've used Advance (formerly in Nashville, relocated to Portland) for bumpers and guards (they are really good, a bit pricey, offer both OE style and show chrome), Tri City in Elizabethton, TN (unbelievable core stock, will exchange or chrome plate yours), S&H in Nashville/Madison, TN - really good work, very reasonable and fairly quick turnaround). Sure are a lot more than I expected to be left in the US,
Powder coating and some anodizing companies listed here, too -
http://www.zycon.com/Products/Plating.htmlRegards,
Steve