@Koro57 You're not missing anything. Until a year ago in PSO2JP, the Rockbear used to be a fixed spawn in the Free Exploration Forest quest, as the end boss in Area 3. But that's not the case anymore. Now there are still several ways of finding it aside from it randomly spawning in as an Emergency Code through several quests.
I sadly don't know which quests are available in the PSO2NA OBT cause I don't have access to it. But your best bet is to do the Time Attack Quest > Marathon Training: Naverius B. Now If I got the the name of the quest completely wrong in the NA version, look for something rather similar as the picture. Pick the Time Attack quest which has the same mobs displayed as below. (Dark Ragne, Garongo and Fang Banther.)
What you want to do in that quest is to clear the first room you spawn in, and then take the west exit! The following room holds a fixed Rockbear spawn. After killing it you probably can abandon the quest and the Client Mission should still be completed. (If it didn't clear the Client Mission, the Rockbear might have been too low level for it to count. Try the quest again on a higher difficulty then.)
(Now if Time Attack quests aren't available in the OBT yet, let me know and i'll try to direct you to other possibilities.)