Why not make it a quest reward? The PC could go on the hunt for a cave/temple/tomb (hidden away or guarded by some creature/spirit) or find another lightsaber user (I prefer the later) and take it from their cold, dead hands. They could then spend the better part of a few adventures "activating" it by exerting their will over it before implanting it into a lightsaber.
It goes without saying the crystal should be RED .
Type of crystal could be Ilum or a Barab Ingot , both of which take a bit of effort to upgrade. It won't matter which crystal you give him since anything with Breach 1 is going to hurt. If you're worried, start the Barab Ingot with Dam 6 and let him upgrade it over time.
Edited by masterstrider