You can try contacting the FTTO. Their details are on the CASA website.
Hopefully they will be more helpful these days and respond to phone call and emails. When I tried to get testing approvals a few years ago, they only had one person handling it and he was off sick most of the time. Then when I could get a hold of him, he told me that I probably won't get approved as there were enough ATOs in the area.
Firstly, they are going to ask you if there really is a need for you to be approved e.g. You a lot of students and ATOs are hard to get.
You will need to do a Professional development program with the FTTO. Here is where you can out about them.
Civil Aviation Safety Authority - ATO Professional Development Program
You will also need to have a mentoring ATO to train you.
Just remember, the approval is now only valid while you are employed with the school. No more Freelance was what I was told be the FTTO.
Hope this helps.
In-cog