surferchick18

When you rescue that old guy on Datooine who is stuck in the sublevels, he will ask you if you want some jedi stuff that he found in the sublevels for 500 credits I think. Buy that stuff and you will get a lens for your lightsaber.

Darth Street

You get it on korriban. At the end of the ruins when you find the dead jedi pick up her remaints and you will get something for your lightsaber (dont remember what) then go to the computer and open the door to outside. Go to the door and you will have to fight the guy that is like made of rock (dont remember his name sry) after you run from him go to the ebon hawk DO NOT ENTER THAT STUPID OLD CAVE OR YOU WILL HAVE TO GET THE LENS DIFERENTLY! Once on the ebon hawk a small clip will come showing all the members of your team gone. Then you fight visas and once you destroy her lightsaber the lens will fall out and you will get it.

crashdummi7

The thing about fighting visas marr (the seer/blind sith) is posted somewhere else like in hints or something but I will post it here to make it more accesable.
Yes you do get all the remaining parts required for making a lightsabre from her once you defeat her. When you fight her depends on how far your alighnment is(light or dark doesnt matter). So make many obviosly good or bad choices to fight her sooner or stay neutral to wait longer