We can't find any source for this item (quests reward, drop, etc). It's highly probable this item is not obtainable right now.
This isn't a 'chest' the 'chest' the other person mentioned is probably a pvp quest object that looks like this image. This appears to be a container in your inventory, rather than an object in world.
I just found this chest. But it's missing the metal lock in front of it and it cannot be interacted with. -Funny enough, it was next to a waterfall and the description mention ''flow''
Where do you get this "container?"