Is there a market in Seoul were i can buy traditional Korean items?

Almost any of the main shopping districts in Seoul will sell traditional Korean items. If there are basement stores, those are the most likely to have the best stuff. You can try Gangnam, Insadong, and Myong-dong for the best shopping. But if you want a good authentic Korean sword, try Insadong. There is an alley way between at the bank at the main 4 way intersection there, where you go down to a basement shop and they have authentic weapons from all over from all time periods.