Celumbra, the Night's Dichotomy

Bought the pattern from tailoring trainer in orgrimmar. For some reason it wasn't available at the trainers in Dalaran. I can only assume it can be bought from the trainer in Stormwind also.

Thank you! Yes, Stormwind tailoring trainer had it.

The cloth situation requires a quest chain & although it appears it is not active yet on live as it requires the Nether Disruptor to have been constructed, but when it is up.. it should go like this:

The quest giver is Eliezer Hammerbeard, located in Deliverance Point in Broken Shore near the inn keeper.

The first quest is called "Fashion History and a Philosophy of Style", just listen to Eliezer´s story.

Completing this quest will give you a new one, "The Legend of the Threads". Just bring him a scroll from Suramar.

Completing this will give you 4 new quests, 3 of the quests takes you to 2 dungeons and a raid in which you must get some materials:
The Thread of Shadow: Defeat Advisor Vandros in The Arcway for Shadow Thread from Vandros' Shadoweave Robes.
The Thread of Starlight: Defeat Advisor Melandrus in Court of Stars for Starlight Thread from Melandrus' Star-Touched Bracers.
The Thread of Souls: Defeat Grand Magisrix Elisande in the Nighthold Raid for Soul Thread from Suramari Soul-Wraps

The fourth quest is to gather 100 Ancient Imbued Silkweave, this item drops from humanoids in Broken Shore.