To my knowledge there has never been a mid air collision in controlled airspace in this country.
I know it's not helpful to come back and say 'but I meant'
But I mean controlled airspace, not a GAAP/Class D Metro, where you aren't subject to a separation service (unless IFR in IMC)
Of the 37 mid-airs between 1968 and 2003:
Fifteen of the collisions in or near the circuit area occurred at one of the five major general aviation airports; that is, Archerfield, Bankstown, Jandakot, Parafield or Moorabbin. Thirteen of these collisions occurred during tower operating hours.
Which would muddy the stats a little.
And of course, Coolangatta 1998
I will have to find this and read it.