I have read that they are part of weapons but dont understand how to go from there. Where do I get the weapons and then how do I get the crystal from them to put in my lightsaber?
You can also get the crystal if you are imperial and PVP:
Crystals (March 29)
Advanced Black-Blue War Hero’s Crystal (+41 expertise) 150k credits, 1950 Warzone Commendations
eta- I would totally use a rainbow saber. My guild leader might have an aneurysm
but Sian would be happy.