The first thing to do is ask them do they export? if yes you must get a Australian Customs import permit from the Police firearms registry in your state/territory you can fill application out but firearm must go to a nominated Gundealer then you must make out a letter or purchase order stating details of rifle, your details, sellers details etc. You then send to Gundealer in USA and he does the rest but beware on what they charge you some charge $300USD to process plus Air courier $600USD to $1000USD! You must tell them to send Air Mail about $100USD and negotiate the processing fee.

A gundealer who does not export is no problem , you tell him to send to a Gundealer who exports (I have a list of exporters) and do the same as above.

A private individual can export they do not have to be a FFL/Gundealer they must apply to US State Dept. for a DSP 5 form fill out and send back with a letter stating they want an exemption from having a exporting licence along with your Australian Customs import permit and your letter/Purchase order once approval has been given the seller goes to Post Office with approval and sends it Air Mail to Australia.

This is basically it there is some fees/tax's which are paid at Post Office when your Gundealer picks it up plus his fee . Hope this helps. I can import for you and do everything just need a Gundealer in NT to send to. Hope this helps.
RLI