Giallo is at Route 14, Rood is at Route 18, Gorm is at the Dreamyard, Ryoku is in the Relic Castle, Zinzolin is hiding in the Cold Storage, Bronius is in Chargestone Cave, and Ghetsis isn't catchable. They will each give you a status affecting TM, and sometimes HMs are needed. For Giallo you will need HM Waterfall and for Rood you will need HM Surf. For Bronius, however, you will be forced to battle two Team Plasma grunts. Once you've found them all, you will learn about N.