Keep your eye on evilbay, particularly local ads where you can both inspect the bike and don't have to pay postage. When you search eBay, do an advanced search and specify 'available to Australia'. This gives you access to the international sites and some great deals come out of Europe, particularly Eastern Europe.

Get onto your bike recycling places - we've got Bikes for Refugees and Bike Kitchen here. They're both your bike co-op type place where old bikes go to get pulled apart and returned to use and can be a gold mine if you're patient. Good bikes are often found in hard rubbish on the side of the road too.

Gumtree seems to be replacing eBay as the source to go to.

Fixed.Org has a for sale section and a wanted to buy section.

Some of the bigger bike shops sell second hand frames but they can be pretty expensive.

Your local velodrome is probably a good source too seeing you're not chasing gears.