Thanks Nikola.
The item id for Easter Firefly Battery in unturned is 6701. You can use this ID with the commands below to spawn the item, give it to a player or buy it on a modded economy server.
Size_X: 1
Size_Y: 1
Size_Z: 0.2
Amount: 10
Calibers: 1
Caliber_0: 6701
Blueprints: 2
Blueprint_0_Type: Ammo
Blueprint_0_Supplies: 2
Blueprint_0_Supply_0_ID: 67
Blueprint_0_Supply_1_ID: 1450
Blueprint_0_Build: 30
Blueprint_1_Type: Ammo
Blueprint_1_Supplies: 1
Blueprint_1_Supply_0_ID: 6701
Blueprint_1_Build: 30