James Robertson's Step Two Designs maintains a useful list of Aussie CMS vendors. Some of them are international, but at least 50 of them are native to Australia. No one can say for sure how well they are all doing, but the depth of the list suggests how easy it remains for consulting firms to get into the content management game with their own CMS applications, especially at the low end of the market. Of course, winning the game is an entirely different matter...
Peruse StepTwo's List of Aussie CMS Vendors