check deposito ferretero or hierro rafa. both are on the main road (from POP to sosua, i mean). hierro rafa is close to that gas station with burger king. deposito ferretero is about 100 meters further.
Beeza, You might want to try the Steel Fabrication shop - I think its called Neos - on the Circumnavigation in Puerto Plata. Quite near the Turn for the Teleferico but on the other side of the road.
They cut some mesh for me and had lots of stock .
We had the bed of our camion redone with diamond plate .. you can ask our mechanic, Stefan - german that lives/has a shop up the hill, across from Charamicos -- he can tell you.