You can use the follows code to get it, If you don't care about which year the data is.
But you may wait for a long time.
AllCitys = CityData[];
AustraliaP = CityData["AustraliaP", "Population"];
ACP = {#, CityData[#, "Population"]} & /@ AllCitys;
Select[ACP, #[[1]] > AustraliaP &][[;; , 1]]
