By "bush hats" do you mean the post-war "giggle" or "boonie" hat or the Hat, Khaki, Fur felt or the "slouch hat"?
The first is hard to find. You'd be better off making some out of putty and sticking it on the figure's head and cutting it to shape. There aren't that many that are made correctly for the Australian version of the hat. It was worn in various ways as well, in the field. Often they used to "bash" the head so that it was inwards built and fitted the head better.
The second is more common but most are not that accurate either. They have the brim folded up (usually only done on the Parade ground) or the brims are too narrow, so you need to careful.
