Metroid Prime 2: Echoes

Which are you referring to the Dark Torvus Temple Keys or the Sky Temple Keys in Dark Torvus bog?
If it's the Dark Torvus Temple Keys, those shouldn't be too hard to find.

If it's the Sky Temple Keys in Dark Torvus Bog, then you'll first need the Light Suit, as both keys are underwater. One in Upper Dark Torvus Bog and one in Lower Dark Torvus Bog.

An easy way to tell which rooms on Dark Aether have a Sky Temple Key, is to locate the Luminoth bodies (on Aether) that have a lore entry. From my experience, there's always been a Sky Temple Key located in the corresponding room on Dark Aether.