Board Thread:Boruto Discussions/@comment-33589845-20171127205023/@comment-734582-20171127222705

Keep in mind that Danzo was the one that orchestrated Itachi's mission. While Obito himself stole a couple of dozen, Danzo had access to the Uchiha afterwards and could've harvested the remaining eyes. This was before he was fired by Hiruzen.

Since Danzo cooperated with Orochimaru, it was likely him that provided Hashirama's cells and the Sharingan. In exchange, of course, for access to said research and powers himself.