If you do not have the full text of a thesis that you need for your research, you can place a Document Delivery request for it. It is worth checking the issuing universitiy's library catalogue and institutional repository first, as many universities make their theses open access online.
Trove contains almost a million theses. Some of these are in print format only, others are available online in digital format. To assist with finding relevant theses the National Library of Australia have developed this guide
OATD.org aims to be the best possible resource for finding open access graduate theses and dissertations published around the world. Metadata (information about the theses) comes from over 1100 colleges, universities, and research institutions. OATD currently indexes 4,571,151 theses and dissertations