There is also the PP at French Bay which isn't big but usually has a few open spots. There are lots of spots at Hilda Lake, no cost but can be busy, there may be a couple spots at Ethel lake campground, or at Crane Lake at Bonida Resort.
Like cory said, try Ethel. First come first serve as far as I know but they had spots open last weekend although everywhere else was booked for the long weekend. There is a campground up by the Marina as well. One of the guys above may have already mentioned it.
thanks again, these answers led me to another web page where i found Baywood Park, nice campsite in early stages of development just to south of Provincial Park campground