Hi Lionheart
I have had no experience in this matter but there is a TV programme on Sky TV in England which is about the Australian Customs Service. (They are very thorough)
Everything goes through scanners sent from other countries and from watching it it will show the shape of a weapon of some sort, and then there's the customs sticker which would have the description of what was in the package which would have to match the item.
My advice would be to check with your Customs Office or maybe you local Post Office to see what the policy is on the transportation of weapons to Australia.
Sorry can't be of more help
Good luck
Paul.