ORCID are unable to provide a full listing of researchers who have ORCID iDs registered to YOUR.DOMAIN.edu.au addresses for privacy concerns.
When your researcher created their ORICD their email address is marked as private by default.
If the researchers change their email address to public you will be able to search for them as follows
Searches of all public email addresses from your domain https://pub.orcid.org/v1.2/search/orcid-bio/?q=email:*@YOUR.DOMAIN.edu.au and https://pub.orcid.org/v1.2/search/orcid-bio/?q=email:*@*.YOUR.DOMAIN.edu.au.
There are methods of retrieving a list of your researchers who have indicated a public affiliation with [your institution]. A number of methods are described here: https://members.orcid.org/finding-orcid-record-holders-your-institution. At the bottom of this page is a form that you can use to request ORCID to provide you with the total number of researchers who have registered and using an email address with YOUR.DOMAIN.edu.au.