I believe that there are a lot of multiple week owners at NCV that either stay for a few weeks or rent the units out. Check out Redweek. There are 367 rentals (full year), most look to be summer weeks. I suspect that many owners don't deposit into Interval because it isn't a lockoff so it's not a good unit to use as a trader, and because the rents are high it makes more sense to rent it out.
You won't see these in instant exchange for sure. Maybe a late cancellation (within two weeks). I look at instant exchange inventory pretty much every day, multiple times per day, and I have never seen summer weeks there. I haven't tried an ongoing search which would pretty much be your only shot, but you will have to trump everyone's trading power to pull whatever gets deposited by an owner. I was able to get a trade for September and had multiple weeks to choose from, including the week of Labor Day, so if you have flexibility in your schedule I would think that would work. September, especially the first half of the month, is usually just as warm as the summer months. (In CA we call it "secret summer" and I love that time of year because the crowds are gone). I frequently see these weeks with a one bedroom unit, rarely with a studio, and they are usually under preference.
I would put in an ongoing search anyway - you never know. If you can expand your timeframe it would be very helpful.