I have left countless links to purchase Windows 7. If you are searching on Microsoft's Australia site it might be a different case there. Though from what I hear your Chinese neighbors can get you Windows 7 for a few dollars... even Aussie dollars.

Update: The Microsoft Store has Windows Home Premium for $119 (http://www.microsoftstore.com/store/msstore/pd/Windows-7-Home-Premium/productID.235488300/vip.true), Windows 7 Professional starting at $199 (http://www.microsoftstore.com/store/msstore/pd/Windows-7-Professional/productID.216645600/vip.true), and Windows 7 Ultimate starting at $219 (http://www.microsoftstore.com/store/msstore/pd/Windows-7-Ultimate/productID.216647200/vip.true).