It's a random drop somewhere in Cyseal I believe. I played more than dozen of times, and have never ever seen one for sale, and so the quantity of one was most I ever had. Bottles of Swirling Mud are almost always in Charla and Hortun's house in Hunter's Edge, one at main floor, other in basement. And I think both always appeared for me.
No use, as mentioned, never found two or more of Hearts.
