In order to get all the cards in Disc 4, you must find the Ragnarok. To do this, enter Grandidi Forest (the forest covered island in Esthar) via a gate. Locate the Chocobo Forest in the norther part of the island. Ride the Chocobo there to Kashkabald Desert (near the Jumbo Cactaur's Island). The Ragnarok is sitting in the middle of the desert.