Replica Legionnaire's Silk Robes should be marked as unoptainable. It shares look with Replica Legionnaire's Silk Tunic, but is not possible to get alliance.

Where exactly is this one displayed? The replica's should be obtainable provided you get the appropriate RBG rating.

Its sold by Tini Smalls <Classic Horde Cloth & Leather> (vendor at Outland - Netherstorm). This NPC sells the "replica" level 60 Horde cloth and leather PvP gear for transmogrification, but only to those with the appropriate old-world title and Feat of Strength, such as Legionnaire or higher. Those Feat of Strengths are unoptainable and thats why this item should be marked unoptainable aswell.

You can get those titles through RBG's though so they are still obtainable.