Scarlet's Game Room
I know of 2 creatures that drop Black Spider. There could be more, I don't have the scoop on ALL the bosses out there yet. I been trying to get Alric to do my work for me - uh, I mean HELP me, but I haven't had much luck yet.
Noxious Gas Golem
Barkingham Palace, Marleybone
Sir Claudas D'Agrodolce (Tier 5)
Grand Tourney Arena (Tier 5)