Could be in Tobi, though I suspect that, if he really is the Elder Brother, he's holding out for the Juubi. Could be in the Gedo Mazo, though I don't think Tobi would let it just sit there. Could be in Black Zetsu, but... yeah, no. Could be in Sasuke, though with his new ocular powers he'd probably just sneer at it. Could be in Kabutorochimaru, but Tobi doesn't trust him enough.

Could be in Yamato. Hmm.