The couple of times I tried booking them myself I had no success on them at all.
My last trip I turned the reservation over to Mickey Travels and told them what I wanted, and they managed to get them. Every. single. attraction. I was amazed. Flight of Passage, Slinky Dog, Frozen, and she told me she could have gotten 7 Dwarves but we were looking at other things.
After that I decided that any future trips I make I'm likely to just let Mickey Travels handle it. I'm not trying to make a pitch for them, but it was incredible how they managed to get everything I was hoping to get, and not cost anymore on the trip. I'm sure there are other similar Disney travel booking agencies as well. It honestly made me wonder if they might have an access or an "in" that regular guests don't when booking. But I was happy to take advantage of it.