On June 5, 2011, Mr Alan Baxter casually threw out a request on twitter for any Australian authors with twitter accounts. He'd conceived of this superficially brilliant notion without realising the consequences - Australia may be small, but there is a huge community of authors, and so he was quickly swamped with enthusiasm. His post contains a good starting list, which he eventually migrated into a twitter list. I believe it's being expanded through comments in his original post.
For anyone who uses twitter and who is interested in following this slowly expanding list of Australian authors, follow here: https://twitter.com/#!/AlanBaxter/aussie-authors-on-twitter/members