A trader in Morek has the best chance to make tons of gold in trading. At one point we were losing 100's of bushels a week to rotting because we had so much food laying around. It has been a while since I saw the hard figures, but I would be confident in saying that Morek produces at least 500 bushels a week of surplus food. Morek hasn't had an active trader in a long time.
Also, what happened to Madina? I see they fell into Anarchy. Is this the beginning of the end?