I was rewatching some of the show, and saw the part where he unveiled his left sharingan. Was this Madara's eye that he gave to Obito, or was it one from the Uchiha massacre? Those were my ideas...
Didn't Madara tell obito that he had plenty of spare sharingan eyes in their hideout that they could use at will? I think in that case he would have an infinite amount
Yah that eye was a spare he got from his sharingan lab. You know that tank with a dozen sharingan eyeballs. *_*
Though what I always wondered was that he didn't really need an Izanagi eye. The Kamui eye was sufficient back when he fought with Konan. All he had to do was literally warp out of the situation.