You can grab some hooded robes around level 40. Jedi Knights suffer from tons of hood-up armor from every single quest, reward and loot. Sith Warriors, on the other part, are bit more "balanced" about hoods up/down sets. As you probably are aware Warriors can get really nice and colorable robes on early levels.
There is one hooded, for example, at the PvP vendor. Right now your best, and actually only, solution is to find something on gtn, from Cartel Packs but you should really just spend those few euros for the Eradicator set for a real Sith Warrior look. :]
for all modifiable gear.