Here's some info people may find useful regarding replica weapons for military costumes.
Doing research for the P90 I'm making I found an ad for airsoft ones for about $25US,thinking "well that's cheaper and easier than making one" I put in an order.As it happens airsoft are considered weapons in this country so can't be imported.
But what about stuff that doesn't fire?
Checking up on firearms and customs regulations I found that " In order to import a replica firearm,an importer will need to obtain the written authorisation of the police firearms/weapons registry in the state or territory where the importer resides,before the arrival of the goods in australia.This authorisation will be in the form of a B709A."
So I e-mailed the firearms branch to see if such approval was likely on this particular replica and they replied,
"With regards to your query re a FN Herstal P90 submachine gun.
Firstly we have no authority to issue approvals for military weapons. This applies to all weapons of this type whether they are air soft, replicas or the real thing.
All of these weapons require the approval of the federal Attorney General and it is only in exceptional circumstances that approval is given.
With regards to decommissioned weapons Customs legislation do not recognise weapons as decommissioned and as such are regarded as firearms and are subject to safety checks. As a result firearms that are decommissioned fail safety testing and are not allowed to be imported."
so looks like it's back to scratchbuilding the P90.
There are some replica weapons for sale in australia,but these are usually types used by the australian army,so it seems locally sourced military weapons are ok but imports aren't,also science fiction weapons based on real weapons and still easily identifiable as such ,like the star wars weapons(sterling submachine gun,mauser pistol etc) can be obtained(not sure if they can be imported though).
I should also add that a lot of conventions don't allow replica weapons to be carried as part of costumes but some do allow them for specific events(costume competitions).
Hope that helps unwind some red tape