...to make sure I strung various words and phrases together properly?
Unless there's some story element that requires an Aussie it's probably better for you to just make your character an American or model him on something you're more comfortable with like a neighbor, client, etc.
But testing various dialog elements can be done well in online chatrooms having themes nothing to do with writing.
You may have to spend some time in some particular Aussie chatroom. You will not only be able to test your lines and various attitudes, but probably pick up some original ideas as well.
But the authenticity of specific expressions is trivial compared to the originality of the concept, story, plot devices etc.