As the OP, I should jump back in here.
The problem is/was not that Patagonia wouldn't take my card. I've used it often to buy direct from them before by phoning them. Trying to buy online though, there's no option to enter a non-US address as the billing address. If you try, it attempts to auto-correct and then rejects it.
I overcame this by entering my Australian address in the AE field, which doesn't autocorrect. They then e-mailed me the next day to confirm/correct the address. I replied to confirm that my address was in Australia and it shipped the next day to a US address.
It still won't ship to Australia, but I have a mate in the US who'll help me out on this one.