From the moment you heard about KotORII having silver lightsabers, you wanted one. (Either that or a red one). You can get a silver crystal easily. ONe easy way I know is on Dantooine. rescue Jorran from the sub-level of the academy, and meet him outside. He will offer to sell you some rare Jedi Artifacts. Save your game, and buy it from him. If you don't get what you wanted, reload and try again. The crystals are generated at random, so you an get whatever crystal you want.