Hey, I'm from Melbourne Australia too.
I'm a girl but I'm training to fight to it dosn't matter where I train, that wont be any good to you.
A few people that box/kick-box for simply fitness go here-->Melbourne Martial Arts - Karate - Kickboxing - Boxing - Self Defence
It's in the middle of the city, so easy to get to, and theres lots of classes.
Depending on where you live, it's probably your best bet. Theres not that much around. Even if you don't live close if you work in the city it's good they early morning classes, lunchtime classes and evening class.
Where do you work and live?