A few blokes with guns and explosives, financed by a wealthy backer or two can maintain a terrorist-style low-level insurgency but a full-on proper civil war with fronts and held territory and everything surely needs either a raid on a state armoury (Libya, for example, was plundered to provide the arms for Syrian rebels) and/or backing from a foreign power. Unless Catalonia has arms manufacturers.
Where did they get their weapons from last time?