If you are looking for a particular standard color (blue, green, purple, red, yellow, silver), you can get them on the Telos Station as you zone into the Entertainment Modual. There is a little shop before you get to the cantina that has 2 guys selling on oposite sides of a wall. The guy furthest from the door sells a random colored lightsaber crystal. If you save right before you talk to him (for the very first time) you can go in and if you don't like the color, you can reload and talk to him again, and VOILA... new color.
Note: you can do this for almost any item at nearly any vendor, as most of them have randomly generated inventories. Just remember to save BEFORE talking to them (not buying from them) for the FIRST TIME. While it may be tedious to reload many times, some may find it advantagous to pick up a Sith War Sword (probably best non-upgraded 2 handed melee weapon in game) within minutes of getting to telos.
