Hotfixes have gone out that fix the issues. The original article has been left below for archival purposes, but we've added a new section above with the list of drop sources.
How to Farm Ascendant Venomstones
After the hotfixes, make sure you turn in the Ancient Depths, Ancient Venom quest at the Silvermoon Catalyst and then Ascendant Venomstone drop from:
Tier 11 Bountiful Delve Chests (Need Keys)
3 Per Full Clear of Tier 11 Labyrinth (Need Keys)
Heroic Nymrissa Wavecaller
Heroic Kith'ix
Heroic Venomous Abyss bosses
First 2 Nightmare Prey Runs of the Week
Bonus Chests from Afflicted and Tormented Souls on Nightmare Prey
Mythic+ 10 or higher.
Original Article
If you've completed the Ancient Depths, Ancient Venom quest, Orin Straylight at the Silvermoon Catalyst will grant you the Ascending with Venomstones quest, which can be turned in immediately. This will unlock Ascendant Venomstone across your Warband and give you your first Ascendant Venomstone, but can only be completed once per account.
Blizzard described how to get Ascendant Venomstones in their official Patch Notes.
Completing this quest will empower defenders of the realm to acquire Ascendant Venomstones, which drop from every Heroic or Mythic raid boss, Mythic+ Keystone dungeons at +10 and above, Tier 11 Bountiful Delves, and Nightmare Prey Hunt Champion gear chests.
Players have now discovered that some of these sources are not currently dropping Venomstones as intended:
Nightmare Prey Hunt Champion gear chests are NOT dropping Ascendant Venomstones.
Heroic Kith'ix is NOT dropping Ascendant Venomstones.
We've confirmed that the following are dropping Ascendant Venomstones:
Tier 11 Bountiful Delve Chests (includes Labyrinth ending)
Heroic Nymrissa Wavecaller
Heroic Venomous Abyss bosses
