You need to farm lv30-40 legendary duelists for them. Lv40 is better for farming SR/UR jewels, because they have a greater chance of dropping rare cards that can be exchanged for them. Gate events, like the current Paradox Brothers, are great for farming them, because it's easy to accumulate lots of keys quickly. If you save up duel orbs, you can farm Standard Duelists for even more keys.
Anoymous
