Go to allakhazam.com and on the left there is a menu. Find World of Warctaft and choose it. Then in the upper right corner there will be a box where you can search for an item. Type in the item name and pick it from the list that comes up. Then under the picture of the item and stats you see some choices and one should be XML. Click that and scroll down until you find <displayinfo>18269</displayinfo>. The number in the middle is the display ID.