The first time that the the trainer dungeon event ran, it required event rations for the first week and they were available from koban only. I the second week of the event, they changed it to them giving you some rations. The trainer dungeon event has run several times since then without requiring event rations.
The first time that the EVO emblem event ran, it required event rations, and they only gave you a limited number. The stages that dropped the EVO emblem pieces could only be challenged a few times per day, too. They've since run another EVO emblem event that gave out enough that I was able to finish 25 EVO emblems.
I expect that it will be something similar with EVO cards. This event will give a very, very limited amount of the missing vol 2, but other events later will make them a lot more common.