Firstly Australia only allows certain species in and most if not all these species are readily available by ordering from your LFS, buying direct from wholesalers, or buying from private breeders. A permit to import fish costs thousands of dollars, and from what I've read you need a large quarantine set up, which has to be inspected and passed by government officials. Australia is one of the few countries which because of strict import bans has prevented introduced species completely taking over the place and new diseases etc from entering.
Why do you want to import fish? if you just want a few, try contacting a whole saler or talking to your LFS owner.