I've done a fair bit of research since my post this morning and it is unfortunate that there is no Aussie rear facing seat that will take you beyond 12kg as apparently it is much safer. And it is technically correct that using a non-Aussie car seat is illegal here. However, if it is indeed much safer, that may be a risk I am willing to take - what's a fine compared to safety???

What I find interesting is that Australia seems to be very strick in terms of the mechanics of the car seat (meaning the requirements in terms of the build and installation are top requirements) but in terms of usage requirements (only allowing the sale of rear facing up until 12kgs), Australia seems to be behind.