I looked at the 1921 - 1985 Victorian Death Indexes and found an Alfred James MADDOX aged 70 died 1931 (Mpna Reg.No.1931/15663),with fathet listed as MADDOX Wm and mother listed as Alice UNKNOWN.
Margaret Alice MADDOX aged 79 died 1938(Richmond Reg.No.1938/11640),father listed as MADDOX Wm,mother listed as Mary Ann UNKNOWN.
On the Queensland Electoral Roll for 1903,it lists a William John MADDOX at Policeman Creek in the division of Capricornia,Polling place of Anakie,occupation as a miner.This is the only William John MADDOX I am able to find on any electoral roll for Australia.
On the 1903 Electoral Rolls for Victoria,there is a Margaret Alice MADDOX and a William MADDOX(either Margaret's father or brother)listed at 347 Brunswick Street,Fitzroy in the division of Northern Melbourne.
On the 1913 Queensland Electoral Roll,William John MADDOX is listed as a butcher at Rubyvale in the sub - division of Emerald in the division of Capricornia.
Thre is no listing for William John MADDOX on the 1922 Queensland Electoral Roll.
There are no births,marriages or deaths of a William John MADDOX on the Queensland Indexes from 1829 to 1910(this could very well be your William John MADDOX.