I've just picked them up from people around forums. Not sure where they originally got them, but my best guess would be somewhere like Smogon since the trade threads there did focus a lot on matching ball stuff last time I browsed that section the other year. There's still quite a few special ball Pokemon (from the Dream World) that I haven't managed to track down I've really been wanting an Ultra Ball Aerodactyl but I've had no luck coming across one yet. Same with Burmy and Kricketot.
Hey, I have everything ready barring the Tirtouga. I've asked my friend if they could breed me one and they said yes, but I'm not sure exactly when that will be (probably later in the week). Do you want to trade the other ones now and then I'll drop you a message whenever I manage to get you a Tirtouga?