First, you should post your information and interests on our Crew Positions Wanted
forum. The best heading, in the Topic line, would be "Australia to Singapore" at the least - start and destination (or, leave start off if you are willing to travel to another country to pick up a berth elsewhere). Then check out the Yachts Looking for Crew forum here as well.
Then, visit your local yacht clubs and marinas and chat up the sailors, find out if there are any boats planning on leaving Oz shortly. If you're not in Darwin or Perth, find a way to contact the yacht clubs there to post your interests.