In short you're right about permanency, the system is very different. I'm a secondary teacher, however I do work in a reception to year 12 school. Supply (TRT) is available and a lot of teachers do it as I know jobs are hard to get. In saying this it all depends on your experience and a bit of luck. Your best bet is to get registered with the TRB first and then look at the schools in your chosen area. On the school websites there is normally a section for TRT work (under employment). You basically fill out a form and register with the school direct. You must have a TRB number, a mandatory training certificate, and if applying at a Catholic school, a certificate for this also.
I did TRT for a short period. I found work every day. The pay was basically around $250-$300 a day (I can't remember exactly). It took me no time at all to get a job, so think positive.
I hope this helps.