OK first off, love Fairy Stone, but we have only camped in a tent there in summer and two trips there in winter we rented a cabin. Schools in many Va counties now are letting out in mid to late May. They started the school year in August and are closing early, so I would look at reservations in June. Campsites with W/E are marked on the reservation system map with reserve america. They are not waterfront, thats all cabins in this park.
Coming in from the North, If you can, try to time it to stay in Floyd on Sat night if you like Bluegrass music, and from there its a short run to Fairy Stone the next day. Also if Fairystone is booked up Philpott Lake is a COE lake with camping also and is only a few miles away.
Temps can be warm in June, and the campground is well wooded so breezes may be hard to find. Temps can hit 90 in early June but generally it's not oppressive that early in the summer.