IIRC there has also been Tropius in a Cherish ball given away at a certain event. I read this somewhere.I think there are only 2 pokes in Cherish Balls as of yet: Deoxys from the Voting thing and Darkrai from the upcoming video...However, using a hacking tool u get Cherish Balls in game...but other than that...No.
You cant get a Cherish Ball in game.