One possible synonym for "Catholic Reaction Force" might be "Catholic Defense League," which could similarly connote a group of Catholic activists committed to protecting their faith and values. Another option might be "Catholic Resistance Movement," which could suggest a more proactive approach to opposing perceived threats to the Church. Finally, "Catholic Militia" could be an appropriate synonym, particularly in the context of groups who have been associated with violent or extremist behavior. Ultimately, the choice of synonym would depend on the specific connotations and implications that the speaker or writer wishes to convey.