GUARDIAN FORCE

Leviathan
You can get Leviathen by drawing it from the boss NOGUE in the Garden Balamb on level B1 on the Second Disc.

Ifrit
You can get Ifrit in the Fire Cave if you defeated him in the battle at the beginning of First Disc and make sure the time limited you chose doesn't runs out.

Shiva
You can get Shiva on the First Disc in Squall's desk in the Garden Balamb when you browse through the tutorial.

Quetzelcoatl
You can get Quetzelcoatl on the First Disc at the sametime you get Shiva.

Alexander
You can get Alexandar by drawing it from Edea on the last battle of Disc Two on the second floor.

Odin
You can get Odin from the Shitora Temple located on the island to the North of Edea's House.

Siren
You can get Siren by drawing it from the boss ELVIOLE in Dollet during the first disc.

Brothers
You can get Brothers by defeating them in the Tomb of the Unknown King located Northeast of Deling City during either one of the Disc.

Carbunkle
You can get Carbunkle by drawing it from the boss SHUMEREKE when you're trying to save Rinoa at the President's mansion during the First Disc.

Bahamut
You can get Bahamut during the Third Disc....Once you have Ragnarok "The flying ship" go to the sourthern most place on the left of the map. A hidden island that looks like an oil rig. (Thanx to Tom Degez for helping me finding this GF)