One thing about armour manufacture - why was so much armour needed? The thing about swords, helmets and the like is that they do not wear out and can last several generations of soldiers. For example modern re-enactment groups will tell you that once you have some chain mail, you never simply discard it because making more is such a swine. Instead it gets used and reused, and woven into different sets of armour.
We know the ancient Greeks had family sets of armour passed from father to son, and I'd be surprised if the legion did not take - or buy- a soldier's armour from him for re-use when he retired. So surely a fabrica was topping up an existing armour supply rather than making new gear for every recruit?