It is not just the mental health system that is seriously underfunded in Tassie @MAMMAFE - the whole Health system here is pathetic. Seriously ill people having to wait in corridors for over 24 hours until space can be made 'somewhere' to accommodate a bed for them - or no beds available at all. People being turned away from lack of appropriate resouces/services and ambulances ramping up to 5 or 6 deep - unable to 'offload' patients because there is no room and subsequently ambulances not available when needed to other call-outs. The government tries to say they have been increasing services and decreasing wait times - but try telling that to those that cannot get a bed or cannot get the help they need! I'm sure you know exactly what this is like!
I presume your son has seen a GP @MAMMAFE - if not that is your first port of call. You can also request an appointment with the school Social Worker or School Psychologist - that is usually done through the child's teacher and Principal. Referrals can then be made to outside sources if needed.
This link gives you a little more info that may be of benefit Child and Adolescent Mental Health Services brochure