Help FFXIII-2: Help getting three Graviton Core Fragments

[Noel]

Well I've been playing the game myself. And I am stuck on getting the last three Graviton Core Fragments: Epsilion, Zeta, and Eta.
I can't figure out on how to unlock the places where the fragments are: Yassif Massif 100AF, Oerba 400F, and Sunleth Waterscape 400AF.

The gate in the Southeast of Academia 1XXAF was Vile Peaks 010AF not Yassif Massif 100AF. The other gate I can't access at the moment.
And I have no clue how to unlock the other two locations. Any tips on how to unlock them? I'd like an answer as soon as possible.

And I don't want to go on with the story till I have them unless it is alright for me to go through Vile Peaks before getting them.
And this would also help my brother and sister who are also playing it.

 

[Master Cat]

Honestly, I relied on the strategy guide when it came to obtaining those fragments - even the regular, non-graviton core ones. With that said, I don't exactly remember the "wheres and hows" necessary to help you out, but I would check on GameFAQs! xD

Sorry that I could not really help you myself... x__x; I'm also sorry if you're the type of gamer who does not like to rely on strategy guides. ^^; If you don't want any spoilers, maybe you can just scroll to that section on graviton core fragments and skim it quickly!