How do you get them?
Well, not pure silver, but silverish. Also, it was bronze, not copper. You have to buy the Mantle of the Force and Heart of the Guardian crystals at the Yavin space station, but you must do it late in the game. That space station has shitloads of awesome gear. If I'm not mistaken, you have to buy it before you board the Star Forge. Costs ~45k, but I found that the money you get for selling items there are very high, so it's not a problem.
But in KOTOR II, you've got these as regular crystals. At least orange, bronze, viridian and silver is available, though those are rare.