YOu can get free evoluters with Tamer lv gift boxes (two sets of 3 and 6). There are also some events to get free evos. Evoluters are also availables at the Core Shop (Kamemon NPC, DATS center) for 50 Cores. And players regularly sells "evo services" between 30 and 70Megabytes. They summon a boss who drops often an evoluter, and you pick it up.