Tailoring quests

Classic

 * The Undermarket (quest) gives a Tailoring pattern as a reward. It starts with the quest Shadoweaver which is given by Nilith Lokrav in the Searing Gorge.
 * Festive Recipes during the Lunar Festival event gives Pattern: Festival Dress or Pattern: Festival Suit.

Legion
As with all prefessions in Legion, Tailoring has its own questline through which you learn most of the recipes.