Thundurus is one of those I just simply clone and pass along. I had to seek a Thundurus myself to get Landorus, and I now have the new formes of them on White 2 thanks to Dream Radar. If you'd like, I can send a clone of the one from my Black game and I won't even ask for anything (though if you have any special babies you've been busy breeding, or any DWFs, I am definitely interested).