That is the Marauder Battlemaster Head Piece. It can only be obtained from someone that can craft it since it was removed from the game. It reguires Valor Rank 60 to wear and is Medium armor.
Just go to the GTN and search Battlemaster and put category Armor then Medium armor and you should see it if is posted. In my server it run from 100K to 150K
Ah man, I'm an assassin and it looks bloody gnarly
are there any other cool masks that assassins can wear that aren't cartel/dramassian? :O