As best I can tell, there are "Jump Off" campsites at the following locations ...
Kiosk, Magnetawan, Rain, Achray and Brent .. and the Kingscote "Walk-ins". 

While these sites are generally  laid out like drive-in campgrounds, they are reserveable throught the backcountry reservation system.

Is anyone aware of any other such "Jump Offs" beyond those I've mentioned?