Here is a specific application for 2009 OSFC in Sydney.
There's a bunch of other stuff in there but there is also some info on requirements and costs to carry a rifle into Australia.

Ooh! This might put you off anyway.
Article recently on Stuff website

Each state in Oz is different. For NSW you need to complete the relevant form from NSW police (P645) pay AU$85 and enclose a swag of docs. The easiest way is to photograph your passport page, NZ firearms license, TSNZ membershhip card. You also need a letter from the organiser "inviting you to compete"
The form has to be witnessed and takes 28 days to process

Leaving the country you need an export permit issued by customs - this is a real pain in the ass if you have to do it at the airport on the way out allow at least an hour for customs to do their bit before checkin.

For queensland you also need a form from their police and pay a fee. Questions are different. Not sure of export process as I left via Sydney. They even count your ammo!

Best suggestion is to go to web site of the police of the state you are arriving in Oz

Sounds like I don't want to get good enough to represent NZ !
...unless it's on our own soil.

An Update .. Ammunition cannot be exported from Australia unless you have it on your permit i.e. if you declared 500 rounds of ammo when you applied for a permit you can take your surplus out otherwise some obliging Aussie will get his paws on it

So for those going to Oceania or Aus Nats declare it on yr permit

Further update after talking to Aust customs on my way out yesterday,

1. For individuals holding a commissioners permit which allows Rifles and ammo into the country you must also fill out an export permit as well, This is generally done at the airport customs area on your way out. You need to allow at least one hour prior to checkin. If you wish to take ammo out of the country the export permit must also include ammo. The max you can take out is what you state on the permit. The relevant form to fill out to export is on the web

2. For a group event such as the Masters games the export portion is handled by the organising committee in which customs has a spreadsheet with the relevant details. Clearence is done at the venue and your case is sealed by customs. Where we fell over is the OC for the WMG did not include Ammo on their documentation

3. NZ part is really easy - go to the arms office with the make model and serial number, flight details prior to your trip. NZ police will check the serial numbers on your entry back into NZ at the airport takes about 5 mins