Where can you find a energy shard in Kingdom Hearts 2?

Serenity Crystlas are dropped by Assassins, Berserkers, Samurai, and Sorcerers. Assassins are found in Twilight Town and The World That Never Was. Berserkers are found in Twilight Town and The World That Never Was. Samurai are found in Hollow Bastion, Twilight Town, and The World That Never Was. Sorcerers are found in The World That Never Was.