You should be able to get a Muisek from any of the hippogryphs in Feralas. After you kill them, target the corpse and right-click on the Faerie Dragon Muisek Vessel in your inventory. Make sure you loot the corpse first because it will disappear once the vessel is used. There is a short cooldown on the vessel, so you it is recommended that you use it as you go rather than waiting until slaying multiple faerie dragons.
<name>, next I must have you capture a creature that in appearance, may look quite fragile, yet its powerful spirit is what we are truly after. The faerie dragons that I speak of have served the night elves as their allies. We must capture one so that the horde may benefit from this strength of spirit as well.
Here is the muisek, <name>. Kill 8 sprite darters or sprite dragons, and capture their muisek. They may be found to the west of here.
Were you able to capture the muisek of the faerie dragons?
Thank you, <name>. Now the spiritual powers of the faerie dragon will be available to us.
I hope you willing to perform another task for me.