Simply as that, I just want to know if it is possible to find all the cards in the last disc or if I will miss some. Thanks!
No, you can find every card in Disc 4 execpt the Namingway, which is present only in Disc 3:
Got from Kuja's room in Desert Palace (near the teleporter, only after Eiko has been kidnapped)
Win from Mario during Treno's card tournament. When the player is in control of Vivi, they are given the option of "going home", or staying in Treno. Choosing the latter will give Zidane a different opponent in the card tournament's second round, who holds the Namingway card.
Anyway, you can check the complete card list and relative location. Only that card seems to be unavailable out of Disc 4.