This site has a fairly complete listing of used flute listings, plus articles on shopping for and buying a used flute:
http://www.jennifercluff.com/used.htm
Some of the flute listings are international in nature. I've been poking around on them over the past month, and I've seen instruments listed for Australia. www.harpsong.org has some dealer listings in Australia, and you might be able to track down some used instruments through them. At a minimum, you should have a repair person ready to check out the instrument for you before you purchase it.
Do you have a flute instructor? A school band director? I would ask those people, too. You might also call the flute instructor at a local college/university when you are seriously ready to buy, and let that person know that you are looking around. University-level students might be upgrading to a professional flute, and looking to sell their perfectly good intermediate flute.
Good luck! --Judy