I think Paypal will still work fine, so long as it is linked to a US address it doesnt seem to matter where the bank is located, which is reasonable as plenty of people do travel a lot but have their main bank account in their home country.
Heck I've even used an AU CC on Amazon with a US address and there's been no issues, so worst comes to worst we should only need to use shipping forwarders and VPNs.
My main gripe though is that we shouldnt need to, it's a pointless tax that's only purpose is to try and make old Gerry and friends happy.
If the AU government really wanted to make/save money there are plenty of ways they could do it without harming the Aussie people, like ceasing unnecessary foreign aid to countries that we honestly shouldnt be helping, but that's a topic for another time and place...