They are random loot for the most part. You can very rarely find them in the base game; blaine sometimes has them. The coretech merchant sells them regularly. They are much more common in the black sea; handmaidens can drop them as loot. I *think* there is a guaranteed location for some; I always find 2 or 3 in this particular spot. Do you know where LemCo is? If so, do you know the map with the big circular submersible room thing that's full of spiderwebs and doesn't function? On that map, between the gas clouds, there is a sliding door you can crawl under. Inside there are a few containers; one always has some for me.
