if you are on the Quest Desert Crawl, given by Castlen Drewe, in PoK. You can only get credit for the Spider Venom Sac by looting it yourself from a desert Tarantula or a dune tarantula in North Ro ONLY. you will not get credit for buying it off Baz... or from looting it off anything else in any other zone.
it is an Uncommon or Rare drop, so don't give up you will eventually get it.
Good Luck!
Edited, Mar 6th 2022 3:17am by Ahmidas