To find an out of print book you can start by getting in contact with a second hand/antiquarian bookseller. One way to do this would be to search the yellow pages for your area. Yellow pages can also be searched online.
A list of booksellers and their contact details can be found from the Australian and New Zealand Association of Antiquarian Booksellers (ANZAAB).
There are also online bookshops and book search databases which may be helpful. Some of these are listed in our eResources under the subject Book Trade.
Biblioquest International (via BibliOZ) have an online search form which you can fill out to request an extensive search for an out of print book.