A new unannounced hotfix for Mists of Pandaria Remix has added new Spools of Eternal Thread rewards to instanced content such as scenarios, dungeons, and raids, granting a large number of extra threads for the cloak of Infinite Potential!
So far, we've found four new Spools:
The Lesser and regular spools appear rewards from LFR and dungeon finder content, with Level 70 characters receiving the normal version and lower level characters getting the lesser. These rewards are only given from the First Day/Week reward.
Greater Spools adding 180 stats are rewarded from world bosses and may also drop from raid content as well, though we have not yet fully confirmed. Minor spool acquistion has still not yet been confirmed.