Alas, today it is all but gone. It has been pulled over to plant cereals or graze sheep. Or it has simply burned. It takes 400 years for a mallee tree to develop hollows big enough for a Numbat to live in. You could try a Mallee National Park.
Hollow trees are the first to burn in a fire.
When land is made a National Park in Australia, all management ceases. The undergrowth builds up. The Park burns. No to find a really old mallee tree, you need to go somewhere that is managed better than National Parks. In fact your journey will end at Yookamurra Sanctuary .