If you visited Georges son I'm assuming this was in England..so maybe checking for George's marriage and birth of child/ren in England.
FreeBMD should helphttp://www.freebmd.org.uk/
You might be able to find George on UK Outbound Passenger lists 1890-1960. (just google uk outbound as Ancestry doesn't allow the link)
It is always hard looking for someone in Australia until we get a hint as to which state they arrived.
There are quite a few George Frederick NICHOLLS on the Australian Electoral Rolls and way too many George NICHOLLS marriages to know if any are him. Deaths in each state are limited with the years that can be searched and he may have well passed after such dates.