Australium was discovered in its namesake country, Australia.
The discovery of Australium has most likely been the cause behind Australia's rapid technological advancement. Said advances in technology include cloaking devices, teleportation devices, and the "entire spectrum of moustache sciences".
Australium is believed to be sold and exchanged within the form of solid bars, similar to the way gold is often reserved and stored. Despite sharing similar appearance properties to gold, such as a similar color and the level of reflectivity, bars of Australium can be identified by the unique logo of a lone figure boxing a kangaroo, one of Australia's most iconic animals. This act of boxing between the kangaroo and the figure is supposedly how Australia chooses their next rightful king.
Australians are known to be very secretive about Australium, most likely in order to keep the element in high value and demand, therefore allowing them to continue to outpace the rest of the world in the technological race.
Australium was also used in terms of payment to Dell Conagher's grandfather Radigan, in exchange for him building Blutarch Mann and Redmond Mann "Life Extender Machines" to further their own attempts to try and outlive each other to inherit all of the land given to them by their father. Radigan Conagher is believed to have found many more caches of Australium, and Dell later discovers hidden files detailing these caches amongst the blueprints Blutarch has lent to him to repair his own "Life Extender Machine".
It has been revealed that the United States once had a supply of Australium. It was all invested in the attempt to launch American monkeynaut Poopy Joe into space before the U.S.S.R can launch their own monkeynaut into space Vladimir Bananas. Following the tragic failure of this attempt, all the Australium went missing. As a result of the incident, Saxton Hale, whose facilities were used for the launch attempt, was brought before a U.S. Senate hearing investigating the disaster. As far as is known, the United States Australium supply remains missing.
In the first part of the six-part comic, Ring of Fired, it was implied that Saxton Hale did indeed steal this Australium by the existence of two hundred thousand pounds of Australium in a room labeled "Mann Co. Monkeynautics". After seizing control of Mann Co., Gray Mann uncovered the safe of Australium, only to find it empty. He deduced that the Administrator was behind the absence of the Australium after finding a cigarette within the safe.