You SHOULD get it from the League of Assassins alert, but since the omnibus was released, loot tables are not consistent. Try there and good luck.
I got it off atrocitus in the coast city 4 man alert but yeah since I'm ibis released loot tables are a mess so can't gaurantee that anymore. Also got the hood off him.
Most stuff that used to only drop in specific places still does - and this is one of them. Largely, what doesn't anymore is stuff that you used to have to do X missions for person Y to get, or rewards that were tied to specific Bounties. For instance, you can still get Scion of Ion, Vestments of Rage, Amazon Polemarch (?) etc. from the appropriate content. But they will also drop as secondary choices (at lower level) in any content (and League of Assassins will also drop literally anywhere now).