It's not quite the same effect, but maybe the alabaster lord's sword?

Go to Siofra Well Depths, and instead of entering the ruins, go to the left. There are ten claymen wielding the harpoon, and therefore ten that can drop it, in a tight configuration. With a wide enough area attack (Radagon's Rings of Light can with a full charge), you can kill most of them in one cast.

Use high arcane/discovery. Marika's Soreseal/Scarseal & Silver Tear mask (if you don't already have a lot), and the Silver Scarab, maybe some Silver-Pickled Fowl Feet.

aoe lightning/holy damage works wonders against the bigger clusters of them

The Poisy Dead