I got really really frustrated trying to get a blue Breed 4 Emerald Proto-Whelp. I used my first dragonkin stone on one. They are still camped on my server, when I finally did get a blue in the wild it wasn't breed 4, and I had had enough. I use Narcoleptic in a lot of Dailies and I haven't regretted using that stone one bit!
I got another dragonkin stone while fighting elementals somewhere. I think it was Deepholm, someone will hopefully jump in to correct me if that's not right. Anyway that's an option if you have pets to level up and have a few dragons you want to stone, since there aren't a heck of a lot of dragons out and about to fight. Good luck!
Side note: the three Wild Hatchlings you can only see at exalted with cloud serpent each only come in one breed. Which I see as a great thing, since if you do find a rare, you know it's the right kind!