Amex has International Currency cards (eg $US)... but I looked on the Amex AU site and couldn't find them.
I agree that it is a lacking part of the Australian market. I'm in a similar boat - living in London so far I've been unable to get a credit card (due to not being able to prove where I live to people's satisfaction), so am stuck using a debit Maestro card and my Australian Credit Cards for some transactions. The forex charges are ridiculous.