I got everything I need on Telos and Dantoine.
I dont remember exactly where I got the parts on Telos but I had two lightsaber parts after this planet. After this I got the rest on Dantoine. You get an essential part from Vrook, no matter if you kill him or not. YOu can get some other parts from the Salvagers near the ruins of the Enclave. One of the female Salvager sells lightsaber parts.