You're in Sydney so digging and lining an outdoor pond is kind of out of the question for you because of your winter weather. You would be looking at a very big pond for them I'd imagine if you were trying to induce breeding. I'd do a literature search in some journals at your local University Library to find out more on their life history. Maybe they breed year round or maybe they are seasonal breeders and rely on environmental cues to begin producing the correct hormones to prepare for breeding. In any case, best of luck to you. Seriously though, Scientific Journals are a good place to start.