Most of the material I used for information on Australian flags and emblems came from two government publications, "Australian Flags" [2nd Edition, published 1998; ISBN 0 642 47130 4] and "Australian Symbols" [Published 2000; ISBN 0 642 47131 2]. Both books used to be available from the Australian Government Bookshops, but since their closure, I'm not sure if they are still in print.
Some of this information is now available from the Australian Government Online Web site, under National Symbols.
Information on state and territory emblems is more difficult to find in one place. The individual state and territory government Web sites generally provide this information, but it is not always easy to find. In updating this material more recently (in 2016), however, I have discovered several websites that now provide comprehensive information on state emblems.
One in particular (the About Australia website) seems quite comprehensive and now provides a lot of material on state emblems that was not so readily available 10 years ago (Click on the Facts menu on the page for any particular State, then select Flags & Emblems on the page that appears).
The Australian Fauna Web site provides information on the fauna emblems, animals and birds, and the Flag Society of Australia Web site has information on flags and badges. You can also find information about the individual state flags and coats of arms by following the 'Identity' links for each of the states and territories on the Aussie-Info Web site.