hey, if its anything like buying rims from japan. you can just use the normal post office (australia post). you have two methods for shipping;
1.air
2.sea
Sea, should cost you about $300 (for 4x rims which weight about 7-9kg yet), you will be look about $600-$800 for shipping by air. (aus dollars)
Here are some helpful Website which should tell you everything you need to know
http://www.auspost.com.au/
http://www.auspost.com.au/IXP/0,1465,CH4030%257EMO19,00.html --- International Services
http://www.auspost.com.au/BCP/0,1467,CH4038%257EMO19,00.html ---Sea Mail Parcels Information
Hope That Helps Cheers Michael