How do you get the Omen of the Iron Inquisitor Icon?
It was sold in the League of Legends store. Riot's description in the client reads: “This icon was released in the store for purchase during 2016.”
Is the Omen of the Iron Inquisitor Icon still available?
Probably not. Riot tied the Omen of the Iron Inquisitor Icon to 2016 (store purchase), and it does not normally bring back past event rewards or bundles.
