The Australasian Digital Theses Program lists Australasian theses
If you do a search on "Choong" you will find the thesis you are interested in listed amongst the results (Number 28). It is not available online from the University of Qld. which awarded it but they do have a service where you can buy a hardcopy
The University of New England, UNE (the Australian one), where Dr. Choong is a staff member according to the link you posted has a copy of his thesis in book form and 3 other books by him in their library. Do a search on "Choong" and "Author" here:
You might also consider emailing him [email protected]
You can join the UNE library as a special borrower for an annual fee and then use their resources, including borrowing books at a distance. If you are a student you may be able to borrow through inter library loan without having to become a special borrower. I'm assuming you're not in Australia...