Citation(s) from the GunPolicy.org literature library
Bricknell, Samantha. 2012 ‘Number of Registered Firearms in Australia, 2011.’ Firearm Trafficking and Serious and Organised Crime Gangs; Research and Public Policy Series No. 116, p. 23. Canberra: Australian Institute of Criminology. 1 June
[T]here were over 2.7 million firearms registered in Australia as of December 2011. It is not possible, however, to estimate the size of either the grey or illicit markets.
The grey market may be substantial but there are no reliable estimates of the volume of it or the illicit market…