Links:

Australian Maritime Safety Authority

AMSA's National Commercial Vessel Hub

The various state-based maritime authorities:
http://www.maritime.nsw.gov.au/
http://www.msq.qld.gov.au/
http://www.transportsafety.vic.gov.au/
http://www.sa.gov.au/
http://www.transport.wa.gov.au/
http://www.mast.tas.gov.au/

Yachting Australia

Yachting Australia's online Blue Book