You find them at monsters around your level. They can be only found on Monday, Wednesday, Friday, and Sunday I believe. Be sure to summon them at the monsters around your level or the monsters won't drop any gems.
@DreamOfSheep Event items don't drop from monsters that KMS does not have. Since KMS doesn't have NLC, none of the monsters there will drop event items. You'll have to go to a less popular training spot to get bells when it's a day for them.
@Fehnle Your example was close for not remembering. Level 160+ is the point where any monster above that level range will give event items.