If you need some Joy Pendants...
The key to obtaining the Joy Pendants (Butterfly Necklaces) is to Grapple attack the Moblins before you kill them or run away from them! By using your Grapple on a Moblin - you're guaranteed a Pendant.
As for finding them - you can always do that Savage Labyrinth on Outset Island to also get a ton of Rupees.
Or (I suggest) going to a Platform somewhere on the Great Sea where there are some Moblins, get their Pendants, play the Song of Passing and repeat...
More tricks, tips and cheats for this game are right here - The Legend of Zelda: The Wind Waker cheats
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