I think the CC group is disc 3 as well, although I started building up a collection of rare cards on disc 2. The boy running laps around Balamb Garden isn't part of the CC Group, but he does have the MiniMog Card, and the Trepies hanging around in the classroom have Quistis' card. Having these rare cards in your inventory will certainly help you on the quest, regardless of when you persue it.