Alright, here is some information for those of you who have not yet heard!
The first obtainable purple color crystal is off of Columi Commendations vendors for Sith.
You used Commendations from Operations to purchase the weapons with the crystal in them.
The counterpart for the republic vendor does not have purple socketed crystals in them, but they have LTBlue (Cyan), and Black/Blue crystals in them already. As far as getting a purple crystal with a Republic character the only known way as of yet is to come across the rare drop within the Vault of Eternity Operation. Also, for the Sith looking to get a Cyan crystal, they would require the same luck in the same Operation. I have seen, in game, players with purple lightsabers, and light blue (cyan) lightsabers already. But only a few. I do know a bit about this, so if you have further questions feel free to ask but I hope this helps, or clears some things up.