I have also found in the 1936 Australian Electoral Roll:
James Graham: Styx River, St Lawrence, Capricornia, QLD: Coal Minor
Jessie Laura Graham: Styx, St Lawrence, Capricornia, QLD
John Graham: Styx, St Lawrence, Capricornia, QLD
These could be mother (Jessie)
So if that is the case....maybe Nigel John Graham died between 1930-1936 in the Styx, St Lawrence region.
Maybe someone might be able to search buriel records for that time and area.