I'm sorry to crush your heart but it's just a myth.
The legend of an Australia began in 1787 when the so called First Fleet departed from England with just over 1480 criminals aboard. The English government were desperate to make some more room in their overflowing jails so they found a rather unique solution. They created the tale of a brave adventurer called James Cook, someone kids could look up to, who discovered a new and desolate land on the other side of the globe named Australia. The government used this idea of an "Australia" to cover the truth from the public that they were executing their criminals, instead of shipping them off to form settlements on a new country/continent.
The English public took well to this idea of an intriguing new land far away, and so the English government was forced to keep up their facade and recruited the help of many other countries to maintain peace among their people. I can see their appeal; a place dominated by desert-like areas that are ready to bloom with agriculture, surrounded by beautiful beaches and tropical coasts in the north-east. Sadly though, this kind of variance in climate just isn't physically possible
Unfortunately rumors of the koala and other "Australian" animals are also mythical. They simply would not be able to survive in such a climate. However the idea of the animal called a koala was based on the bear sub-species called a drop bear (Ursidae Desendrare). Drop bears have recently become critically endangered and can now only be found in South Africa. Unlike how a koala was mostly described to be a slow and sleepy animal, drop bears are dangerous, carnivorous predators and should not be approached.
I understand this must be difficult for some to here but the legend of an "Australia" is just a myth. You deserved the truth.