In Oz, there's only a handful of places that will ship live fish. Plants are a more popular things to send via the mail, but if you're in the state of South Australia, you're out of luck due to the quarantine laws.
Two of the better guys that will send you fish in the mail will give a money-back guarantee. That's kinda nice and reassuring.
I've not yet done it myself, but I'm about to order glass & ruffle shrimp from a place in Darwin. We'll see how they turn out.