Your chances will depend on you.
PHS and The Helicopter Group do employ ex students, but it mainly depends on the type of person you are.
Are you good with people, can you drive a mini-bus, what are your office skills like, are you engineering minded, do you have a great attitude, and are you a hard worker? They will look at you while you do your training and keep you in mind when the next slot comes up.
I can only speak for PHS, but usually the guys that had all of the above got a chance in the end. Doing the "Hanger Rat" stint in Melbourne is required first though, and this is where you get a chance to prove yourself.
Cheers BM