I understand that ASA opens the "recruitment window" for a limited period via the internet and unless you are checking regularly you may miss out. Try ringing the HR area of either Brisbane, Melbourne or Canberra ASA and talking to someone in the know.
For what it is worth, if you're young, fit and looking for a great start to an ATC career, consider the RAAF. I've done both sides and as a younger guy, the RAAF was great. Good luck