July and the first half of August are very high demand periods. The closer you are to the date, the harder it gets and since the exchange window is now open (less than 8 months from August), owners at all resorts are now vying for whatever opens up. On the other hand, the original owner can now request any Hawaii property so as Denise said, you can open up your search parameters to include any arrival day at any of three resorts: WKORV, WKORV-N and WPORV. I think WPORV would have the highest chance of being available. The other too are probably going to be hard to get and would likely involve getting placed on a waiting list that might not clear. You might also end up in an Island View unit facing the parking lot at WKORV.
On the other hand, this is the benefit of owning where you want to go. Once you do buy WKORV-N, you will be able to reserve at 12 months out, even if 2009 doesn't work out right now. I usually travel around the July 4th holiday and have never had a problem getting a unit there as long as I reserved between 12 and 8 months before arrival. Given that you are restricted by school holidays, you really don't want to bet on exchanges coming through at the 8 month window.