Brigs don't carry much I have noticed. But if you go to the south portion of the map, you will begin to find frigates and man o wars with 100, 150, and rarely 200 resources. Usually one crafting resource (ie metal, wood, cloth) and one money resource (rum, sugar). The man o wars sometimes even have a thousand reales plus cargo.
I am the FrooFather, and I approve this message. PSN: KJIcemanXiahou Alt: Froofather