My 2c
I think you would need to convert to an Australian CPL first before you can start an instructor rating course. I don't think that would be a huge hurdle if you were serious about working here. The CPL theory exams are not at ATPL level.
You also would need to pass a CPL flight test. Depends a bit on your training and experience as to how close you are to doing that. (The flight test is basically done as a pretend 'charter flight' where the instructor will give you a task to fly to several destinations then introduce some difficulties and changes during the flight, test your flying skills are within tolerances, check your ability to handle problems and make sensible judgement calls and test your ability to operate in various airspaces, all to a sound level).
You probably could organise to do the flight test (and preparatory work you may need leading up to that) with the flight school where you would be doing the instructor rating prior to starting the instructor course.
I also assume you have (or are confident you can obtain) Australian residency? You obviously will need the appropriate rights to work in Australia.
My opinion is if you are enthusiastic about instructing, show good aptitude and potential and relate well to people, I think you certainly will get work here. In demand Instructors have sound skills, relate well to people, have a competent and calm manner in the cockpit and have a passion for teaching. If you show that, you will do well. It is not the most well paid (or glamorous) end of flying but if you enjoy it, it can be very personally rewarding.