Keep in mind that this is a different state so could work a bit differently. We had ours installed by our mechanic who is also a licenced with vicroads child restraint fitter. They contacted Holden (we have commodore wagon) and they quoted a genuine holden dic-kie seat which cost at least 2.5k so we got one from eBay for $500 (someone bought a wagon with one in and didn't want it...go figure we couldn't find one with the seat already in it ) and they then installed it for us. It cost us about $1200 all up.

DH found a couple of aftermarket seats too that we were close to getting. Nice ones that folded up to the sides. I'll ask if he still has bookmarks and will let you know if he does.