The second robe looks almost identical to one of the sith you fight on Malachor V. It is kind of like the sith assassin wtihout the mask. I'm sure it could be done. The first however seems impossible wihout modeling.
I searched for the sith robe but I couldn't find it. I replayed the malachor V and it does resemble the one used by the really good sith lords. Sorry I couldn't be of anymore help.
Edit: I found a file that you might like. Here is the link.