This activity can be acquired from a fisherman in the camp north east of Uzhitz, as seen on the map below.
Speak with the fisherman to ask about fighting in the region. He will refer you to three other people before he will fight you; Josef, Maple and Mash. You can find each of them marked on the map around Uzhitz. Once you have beaten them you can defeat the fisherman, and thereafter speak with him and the others whenever you like for more fights.