Where to buy screw mount cameras and lenses

In all the usual places where you would look for the second hand equipment. Local newspaper "for sale" column; second hand shops such as Cash Converters; many photographic stores have a second hand equipment section. If you are in Australia a good place to look is the "Photographic Trader" magazine and a local "Trading post" newspaper. Many information is available on Internet.

Australia

Canberra Times Classified, for sale section
AllClassified web site in Canberra
Fairfax Market (Not much usually)
News Classifieds
Trading post online

Australia Auction sites


The most popular is, of course, the EBAY
Others:
Stuff.Com

Sadly, not many Australian shops put their second hand stock information online.
A good place with regular updates is PhotoCo
See also: European Cameras
Mainline Photographics
Plaza Cameras
Camera Electronics

Teds has a "preloved" sction on it's web site, but doesn't update it very often.

Internet Links

That's completely different situation. Many shops specialize in the second hand photographic gear.
The impact guide have a good number of links to the second hand equipment shops.