From the Dark Wraiths?! I am about to try some Slab farming there, how rare are the drops? I am on 410 item discovery.
I was farming for chunks with 410 item discovery and ended up with 3 slabs in a matter of 10 minutes. I went back later and over an hour got a few chunks, a ton of dark hands and no slabs. So chalk it up to luck of the draw.