If you are already at the World that Never Existed, you are out of luck. Dancers can only be found right after Proof of Existence. 4 for every world refresh, and they come paired with 4 Samurai and 4 Berserkers. Drop rate is a mere 8%, and they are the only ones that drop Twilight Stones. Lucky Lucky improves the rate to 16%, which means, if you are lucky, you will have to kill 6 Dancers, which means 2 or more world refreshes, including the fact you have to kill the Berserkers and the Samurai at the same time.

Havoc's Divide and Addled Impasse do not contain Dancers. I've seen a few in Passage of Creation and Ruin, but they were few, far in between, and were mostly assisted by Sorcerers.

I never used to have a problem with Berserkers and Sorcerers until when I hit level 70...