He says he is an international student, so he won't have any pull with the local politicians. But if neither CASA nor the local cops want to become involved in what appears to be a minor (but important, to him) property dispute, maybe he should make some noise with the local media about how, yet again, foreign students are being jerked around by ratbag Aussie schools.
Overcharging and under delivering, witholding legally required documents as per the CARs etc.
Call the school and deliver this ultimatum: hand over the logbook today or be prepared for some free publicity tomorrow. Because it has 'aviation' in it, one of the TV channels is bound to be interested in running it on a 'name and shame' evening program. All the better if he plays on the foreign bit, and how he chose Australia for his training because he believed it would be the best available, blah blah, only to be so sadly disappointed in the lack of ethics, blah blah.
Provided he only speaks the truth, he can't be held for defamation - at least that is my understanding.