At this late stage, most caravan parks are probably fully booked for most of the holidays... Lots of National Parks don't take bookings so you could try your luck there. There's also some "primitive campinggrounds" that work on a first come, first served basis.
It's a very broad area you are considering, so hard to give recommendations. Also, most of our favourite spots, we've already covered in the Park & Recreation Area Reviews or Camping Tips and Locations areas. Just have a browse there. You might also be able to find some nice pics in The Great State Photo Comp.