The film crew first traveled all over the country in search of filming locations.
Literal
Film-crew [topic-は], first filming-location [object-を] seek-[and-て] that country-inside [object-を] traveled.
Film industry vocabulary. 撮影隊 ('film crew') uses 隊 ('team, unit, squad') — a military-origin counter-suffix for organized groups. ロケ地 is a contraction of ロケーション + 地 ('location place') meaning 'filming location, shooting site' — industry jargon. を on 国中 marks the path/area traversed, not a direct object (typical of motion verbs).