All of the major cities in Australia have a number of talent agencies looking for potential stars in the making. For those in the city of Melbourne, it seems like it is particularly prevalent. A Melbourne talent agency is going to be able to spot younger people and potentially make them into stars.
In many cases, a talent agency is not going to be open for tryouts. Instead, they are going to be on the lookout at all times, and they are going to be searching for talent out in the public. There is really no rhyme or reason when it comes to what they are exactly looking for, but they have been able to find some young stars in the past.
If approached, always ask for credentials. They usually are going to be more than willing to help out and provide information to show that they are legitimate.