They were farmable off of the plague babies in the last part of the swamp. Also the giants there I think, but those weren't worth farming.
Black tendancy earned you more souls and loot, so if you could handle it it was worth the risk. White tendency was hard to get though. The only ways to get it either involved multiplayer, or killing bosses/primeval demons which of course only show up once per play. Since certain unique items required pure white it was easy to fuck yourself out of them.