Best place for aussies to get stuff from UK is bookdepository.co.uk . But they don't seem to have zombicide at the moment from what i can see.
Also try milsims.com.au if you want to buy from an aussie company. They are in melbourne and have awesome prices and shipping rates within australia.
I don't think that bookdepository will ever have zombicide, because it looks like they only sell FFG games.