"[a]cademic estimate, this amounted to about 20 percent of all privately owned guns in Australia."

So, this leaves ~ 80% still out in the population with gun types across the spectrum.
The number of unregistered guns in Australia is unknown per link and there is a trend toward more use of handguns..

Link: https://www.aic.gov.au/publications/tandi/tandi361#:~:text=Firearm-related%20crime%20is%20relatively%20low%20in%20Australia.%20However%2C,used%20to%20commit%20most%20handgun%20crime%20in%20Australia.