John C Downie is the brother of James Downie, several of whose books he illustrated, including Warrigal, the Story of a Wild Horse (1935), Killer-Dog, and The Treasure of the Never-Never (1936). He has written and illustrated at least one title himself: Galloping Hooves, a Story of Australian Men and Horses.
Finding the book
Reasonably easy to find.
Austlit – the Australian Literature Resource