If you want the exact value for your location, go to
http://www.ga.gov.au/oracle/geomag/agrfform.jsp and fill in the boxes.
For here that gives D = 12.430 deg changing by -0.002 deg/yr
If near enough is good enough, there are links to JPEGs for all of Australia a bit further down the page.
For Marnoo (location from
http://www.ga.gov.au/map/names/)
Requested: Latitude -36o 40' 0", Longitude 142o 52' 0", Elevation 0 km, Date 2009/12/15
Calculated: Latitude -36.6667o, Longitude +142.8667o, Elevation 0.00 km, Epoch 2009.9534
Magnetic Field Components
D = 10.290 deg
dD = 0.012 deg/yr
Andrew