...or is the closest thing to it the one and only Xenotech weaponmasters vest?
In late beta, they switched a lot of the armor models for Jugg and Mara. Maras used to have all the hooded robes. It's kind of silly, considering Sentinels have a few different hooded robe options, while Maras have none. The only "robe" is the red Xenotech one that drops in KP SM.
The PvE chest (Tionese/Columi/Rakata) has a hood if you hide the helmet or choose other helmet options. This isn't a robe though. The PvP chest also has a hood, but again, not a robe...but it is black. Those are your only other choices.