this will be the 3rd post trying to explain to you how it's done, hope it gets thru
Each npc has a number for identification, find it either thru shift clicking or searching for its name if it is unique. After you find this number you can easily find the corresponding htmls that are used for interacting with it thru dialogs. Inside those htmls you will find a number followed by a multisell keyword, that number is the name of the corresponding xml containing the multisell configuration. Ingredients are what the npc takes and production is what the npc gives back for each entry in the multisell window. They told you the paths those files exist in so you can't complain it is hard.