There's a few main ways to get Itachi, however the most common is usually buying fragments, or if you have Naruto-level luck, the Seal Treasure. The main places fragments for Itachi will possibly show up is either what Kfactor stated, about how it'll possibly be in a future minigame/ update, or through the Black Market Merchant. I'm pretty sure there's no instances where you can get Itachi, or any Akatsuki member fragments at all, without either being lucky, want to spend a LOT of money on getting seal scrolls, or just being patient. :victory: