Hey Stuart. I see 4 options for you:
1. There's a copy in the GeekMarket
from Europe which will send worldwide and shipping, in that listing is noted as 18.99EUR
2. Use a service like ShopMate
to on-forward your game (assuming you buy it in USA). ShopMate is NOT cheap - you should expect to pay at least $40 but probably $60 (or even more depending on weight and size of the packaged game). It's a service I have used before and they are fairly quick and efficient, but the cost makes it an absolute last resort. If you use them before the end of the year there's a 15% discount promo.
3. Find a friend/geekbuddy/relative/someone who will accept your game and on-send it to you via USPS/UPS etc
4. Wait till it comes out in Aus - you could email a few of the larger OLGS's and see if they are planning on getting it in or whether they could get a copy in for you.