It's in CAW.
Ten km from the Info Centre, turn right. Three km of dirt road to an ENORMOUS area for free camping, right on the Darling River.
NO FACILITIES! You MUST be totally self-contained.
Great walking tracks, and if you're game to tackle the steep gully to the left in your vehicle, more campsites. High-clearance 4WD recommended... there have been LOTS of towbar scrapes at the bottom.

There is a mob of resident kangaroos who seem to tolerate humans on their grazing paddock, but will bolt if you get too close.
Dogs OK, but keep them on lead, for the kangaroos' sake.
Warning: Dry weather road only. People we spoke to had been there after rain. Black soil quagmire.
Here's the map from the Info Centre: