A couple of other nice spots are Kettle creek at the bottom of the Okanagon and Christina Lake (about 1 hour east of Osoyoos). We stayed 2 nights at Christina lake on our trip back from Yellowstone and it's a very nice campground with great swimming.
Another very pretty Prov Park is Kentucky Alleyne Provincial Park. It's a bit of a drive off of 5A and we were going to skip it until we hit Kentucky lake and then we were blown away with how nice the view was. The drive to/from Princeton is worth the drive alone.
Of the 3 Kentucky Alleyne will be most likely to have spots but we have fluked out on every trip and found spots at all 3.
Kentucky Lake BC Park Site
Let me know if you need any more info