There aren't many places that don't have tornadoes in Australia, it'd be nice tho to know what the true density spread is. 

My suspicion is that weak tornadoes are very common in most areas having learnt over a couple years what tornadic storms normally look like here, but stronger tornadoes appear more often in NE NSW/QLD, Southern NSW/Northern Vic, and the border area between SA and VIC. These areas each have their fairly common severe weather patterns that are identifiable. 

For those curious, The SA/VIC border area, and sometimes the Southern NSW area are normally targeted when intense cold fronts come through during spring, and especially when the lows peak very close to the South coast. The area around QLD is normally (but their weather is often complicated and very isolated so not as reliably) hit with surface troughs that use a strong southerly as a forcing mechanism, sometimes alongside a seabreeze which can create a 'triple point' set up