Head to Toto Lake, northeast of Zora's Domain, at the top of the dam: use the Zora armor to climb up the waterfalls like a salmon, then examine the surrounding ruins. Behind a pillar, you will find a chest placed underwater. Stand on a ledge to use Magnesis in order to recover the chest. This one contains the Zora helm.
Zora armor
Little to say about this one: follow the quest of the Zoras and the divine creature Vah Ruta and you should get it very quickly. With this one, it is possible to go up the waterfalls.
Zora greaves
You will have to complete the additional quest "Lynel Safari" for Laflat: the goal is simply to take a picture of a Lynel. If you have defeated the one who showed itself during the preparation of the Vah Ruta assault, you can always go to Lanayru's eastern access to meet another one for sure (and recover the associated memory if it is not already done).
Written by Bastien "Lloyd" Dubosq-Luyer. Translated from French by Millenium.us.org.