I am an apache pilot... trying to find a job as a mustering pilot
Interesting career move indeed, but why not!
You will have to get experience on the ground first for anyone to hire you to fly, as you can't be a mustering pilot without first knowing how a cattle station and a mustering operation works (this may have been different 30 years ago, but nowadays there are plenty of mustering pilots around).
So first you will need permission to work in Australia. Go to a flying school, convert your license and get rated in the R22 if you aren't already. I hope you have some experience in smaller single engine machines, otherwise this might take a few hours. Next, apply at any of the larger stations for a job as a station hand. If you aren't afraid of getting your hands dirty it shouldn't be too hard to find work, someones always looking out there. Work on the ground for a year or so, learn how everything works, and if you aren't useless you will probably meet someone sooner or later who will give you a go at a flying job. It's all by handshake and word of mouth out there.