They only drop from the chests that spawn on random nodes of the map and have a really low chance of occurring.
Have a Romancer in your party and equip the Player Books + Chicken wings in the Metashop. Go to Tanton (the starter planet) and fight two battles of 6 elite enemies and that should guarantee a chest spawn on the map. Hope to your respective deity that it's an artifact and rinse and repeat.
Your player level doesn't matter so bring any party that can deal with these fights as fast as possible. I recommend a Savage with lots of initiative so that you can AOE with Global Rage all 6 enemies. And put something on in the background cause you're gonna be grinding for hours.