Agree with Famn completely. I too am out of the loop a bit as my children are older 5 and 7 years old but we also had a Safe n Sound when they were smaller. It of course also depends on how old your child is etc. I too would wait until you get to Australia and then just go straight to a Target or K-mart or somewhere like that.
Australia has different standards for car seats and ones bought here or in the UK may not be acceptable there. The standard there is to have an anchor point, so I would suggest buying in OZ. Have a look at ebay.com.au to see the types currently selling.
www.babyzonedirect.com.au
www.babyland.com.au
and toys r us are some of the retailers... along with Target, Kmart, Big W..
I am 5 years out of the ozzie loop so can't tell you current brands. Mine were safe'n'sound brand.
Hope this helps!