Go to the
CASA website and it'll have the info you need regarding converting or using a JAA PPL in Oz. Note the bit about getting a form from the CAA.
Have a look
here for an example of a popular school at Sydney, Bankstown.
If you prefer a smaller organisation try Liverpool
FlyingSchool at Hoxton Park. A smaller aerodrome near Sydney.
I have used both for different parts of my flying and worked at LFS.