I'm going in September and I booked all my ADR's in March. Decided about a week after making ADR's that we did want to try Le Cellier, and couldn't get an ADR.
I kept trying, nothing popped up. Finally got a 4:00 p.m., not what I wanted, but hey, better than nothing.
I started reading some of the trip/food reviews and saw how you can eat at the Rose and Crown before Illimunations and either sit outside or they will bring you to a viewing area. This intrigued me, so I went and found a 7:25 for Rose and Crown and ended up cancelling Le Cellier after all. I posted the cancellation on here so hopefully someone was able to get it. (By mistake, I posted it here instead of on the reservations thread, ooops, but I did post it!)
So, keep trying, I never thought I would have given up that Le Cellier reservation. Your not going until August, so something is bound to pop up before then. If not, find something else you would enjoy, book that, and if you happen to get Le Cellier, bonus!