So that's fragment one and two. Now you need three.
Unless you are or have unlimited access to a friendly rogue with 350 lockpicking, you'll need the key to Arcatraz. Like Strat Dead or Scholo, only one person in the group needs a key, but unlike Strat or Scholo, if you die inside and release, you end up alive, in the graveyard, needing to be let back in. Relying on the single key bearer to die with you seems a little harsh, doesn't it?
So, you should have done the Assisting the Consortium quest line and should be up to How to Break into Arcatraz. You have to be either a 68 druid or 70 since you can't get to Tempest Keep unless you can fly. Do Mechanar and Botonica to finish the questline, and now you're ready for Arcatraz.
Arcatraz is the hardest non-heroic five man dungeons in the Outlands, but you don't have to do the whole thing to get the fragment. In fact you can skip the first boss, go straight up the ramp, clear a few elite voidwalkers and grab the fragment to the right after the tunnel. Again, if you can find a group that has cleared but not taken the fragment already, you can join, run in, kill the spawn and get the fragment.