Here you go guys, the one I've mentioned time and time again...The Nebilim Battle!
Here are the locations of the Devil's Arms;
Evil Eye (the chakram) Is in the Toize Valley Mine. Crush the Naploosa Bacura then go search its remains.
Abyssion (the twin swords) Is in Flanoir. Talk to Abyssion the person near the church and he gives it to you.
Fafnir (the dagger) Is in Gaoracchia Forest. You'll find it in a chest in a plant-dome thingy near to where you fought Regal.
The Gates of Hell (the card) Is in the Earth Temple. After finishing the Earth Temple, go back to Altessa's place and talk to the Gnomelette there. Then go back into the temple, past the Dragon encounter, a little cutscene will occur, and then it's in a chest past where the Gnomelettes were standing.
Soul Eater (the single sword) Is in Triet Desert. After you are able to travel freely between the worlds, go back to Triet Oasis. First talk to the man near the upper exit of town, he's near a shop. And then go up to the Oasis and talk to another person, he'll be standing near the water. After talking with both of them, go out to Triet Desert, go behind a mesa on foot and there will be a skit-like ring of blue light, that's the encounter where you get Soul Eater.
Disaster (the kendama) After you complete the events regarding Alicia's death, go into the hotel and stay the night. When given the option, say you want to go outside. Then take the tram and go to the casino area. Once there, go out onto the bridge-like area and talk to the man standing near the edge, and he'll sell you the Disaster for 1,000 Gald.
Diablos (the axe) Is in the Latheon Gorge. The chest is near where you come back up if you fell down near the waterfall. You'll pass the chest no matter what, so keep your eyes open and you'll find it.
Apocalypse (the greaves) Is in Welgaia. Go into the building near where you get the Mana Fragment, and go into the door on the left on the first floor, the chest is in that room.
After you collect Apocalypse, go and talk with Abyssion, and he'll tell you that he'll be waiting in the Temple of Darkness. After the cutscene, go back to Sylvarant and talk with Koton on Hakonesia Peak, and he'll give you the final Devil's Arm, the Heart of Chaos. Then go down into the temple of Darkness to where you fought Shadow, and he should be there. If not, come back after you've gotten the Derris Emblem.