The ranged weaponry niche occupied by bows and slings in most other parts of the world was in Australia occupied by boomerangs and woomera (spear-thrower).
These wouldn't have had the long range of a sling or bow. However, that longer range has to be achieved through 45-degree ballistic shots, which is really most relevant for massed warfare. As hunter-gatherers, they didn't (and likely couldn't) often get together in the kind of numbers that would have made an enemy ballistically firing into their mass at range the most effective tactic.
They did have their own advantages. The aerodynamic shape of a boomerang meant it could travel on a relatively level plane for about 100 meters, which likely meant a single shot at that range from a skilled thrower is more likely to hit. The woomera-launched spear had four times more stopping power than an arrow fired from a modern compound bow.