The Druidic Breeches are found in Kesh Corann. You’ll need to find the entrance to the cave then make your way through the camp until you reach the chest where you’ll find the breeches. You’ll likely need to battle your way through this area as it is heavily guarded by Druids.
You’ll find the Celtic Armor inside a locked house in Rathcroghan. You’ll be able to obtain the key from the Chieftain elite enemy that’s standing guard on the tower nearby, you can use Odin’s Sight to distinguish him from other enemies via the key icon above his head. Once you have the key you’ll be able to grab the armor from inside the house.
The Celtic Breeches can be found in the northern part of Cashelore fortress. You’ll find the chest containing the armor behind two movable barricades. You’ll first need to move the smaller one inwards, then you’ll be able to shift the larger one to the left to make a small entrance into the room. At the end of the room you’ll be able to grab the armor from the chest.
The Ceremonial Sickle is found in Lackanscaul, which is a Druid camp west of Clonfert Abbey. You’ll find the chest containing the weapon in an alcove at the center of the camp. You’ll likely need to fight a few druids but you can be semi-stealthy in this area as the enemies are fairly spread out.