That's actually not a problem. I'm in europe and I've bought like 7 games off of the US PSN store. You just need to make a US PSN account on a new user, then you fill that account with money by buying cash cards online. The stores email you the codes within minutes, and you don't lose a lot of money by doing it. Depending on what games cost in Australia, you might even save money by buying games from the US store, even if the stores that sell the cash card want a tiny bit of money for themselves.
If you use gmail, you don't even need to make an additional email account for it. You can just make another pretend-gmail address that shows up in your regular gmail. All you do is enter whateveryourgmailis+somethingelse@gmail.com when PSN asks for an address and it'll work. You'll get those mails sent to your regular gmail account.
Personally, I just used "+psnus", to keep things simple and easy to remember. I have a "+psnjp" too for access to demos and stuff when they are released in japan. That store is a bit hard to navigate when you can't read japanese, though.