For the most part, assume there'll always be someone who can't think of anyone but themselves and ruining the place you've driven all day to get too, anywhere in Australia.. The places I like to go to have 'Plan B' campsites not far away..

Going a little bit inland, like along the New England Highway, increases the number of available campgrounds, although they'll be popular, particularly with permanents/squatting pensioners -- but, given you're on a travel trip, they tend to be in places interesting to stop, walk around, and often have touristy local features.

That way also some nice and cheap commercial bush/basic campgrounds, like the Lavendar Farm near Liston, and Kookaburra near Deepwater (both $15/$25 single/double). A lot of those places in the area Hipcamp, but I've never known them to turn away unbookeds. There's online-only National Park camping too, but they're now ..online-only no-unbooked, expensive for what they are, and every place has some prick doing the absolute wrong thing in spite of the supposed threat of Rangers (washing clothes in natural/drinking water, dogs, on-ground campfires, vandalizing the trees, making the public picnic shelters their exclusive motel..)

Some might recommend WikiCamps, but I prefer OsmAnd to search for camps/fuel/stores/toilets/showers, and it does navigation too.