North iberians (Catalunya) have used Celtic type of Montefortino helmet, especially iron type: There are native version of Montefortino helmets in Iberian burials (round points on the map), exclusively in bronze:   The only possibility to use others Celtic helmets is for a regional South Aquitanian unit (Iberic/Basque speaking). It is possible. For the Celtiberians, I don't know if the team want to solve this issue yet or if we just add Celtiberian merc units