HBT supporter Wild Hops Print Shop has gold ones with your logo on them. Maybe email them and ask if they'd be able to get / do / sell you blanks of copper?
Found this thread, thought i'd chime in. Unfortunately, I'd have to buy 500,000 caps to get a new color. This is the second request for a copper color though, so i'll keep it in mind! For now, you'll be stuck with spray paint (personally I don't like the idea of the trace amounts of overspray that will get under the cap getting in my beer!).