Ultima Weapon: Recipe is sold by a moogle shop in 000, check moogle shop sticky on the boards. The other materials needed are found randomly in chests in either Solitary Salvation or Pervasive Sorrow gateways.

Excalibur: Drop from level 100 Vicious enemies in free battle (Gabranth works), but the drop rate is very low. You can also craft it in shop by first buying the lower-level swords.

Genji set: Buy Heike's set from moogle in Scenario 000 (again, sticky). Buy Samurai Spirit from the secret moogle shop in the Lands of Discord. Then get Gilgamesh's battlegens (must complete Report #19 first).

Lufenian: Found in many treasure chests in Scenario 000. The easiest place to farm is the Conquered Trials gateway. 4 red chests always contain a random Lufenian piece. The middle chest is guarded by a level 127 manikin; the rest are all just level 80 manikins. You can keep exiting and re-entering to make the chests respawn, getting as many as you want.