NOTE: To make sure this works correctly, you must have 1, and only 1 of the items to duplicate.

1. Set up a proper unit: Build a unit that has at least one person who can only carry one item. I normally use a unit made up of 5 wizards to do this. Now you need to set up the items. Make the unit use up all but the last two item slots, then add the item to duplicate to the very last spot. It should look like this:

(Random Item)
(Random Item)
(Random Item)
(Free Spot)
(Item to Duplicate)

2. Remove the charcter and the item: Ok, now, just remove one charcter (that character can only carry one item). Now your items should look like this:

(Random Item)
(Random Item)
(Random Item)
(Item to Duplicate)

Go to the carry item screen, and remove the item to duplicate. That item should now be saying 55/01. Leave the edit unit menu, and go to the item menu. Now you need to sell 2 of the items. It should look like 55/54 now. Now sell 56 of them. It will now say 55/98. Leave the item menu, and exit the Orginize Screen. Reenter the Orginzie Screen, look at the items, and it should say 00/98. You now of 255 of whatever item that was.