The /isearch command is incredibly useful for finding potentially misplaced items. It also works with partial strings, so "/isearch mon" or "/isearch mask"(without the quote marks for either) would give you a list of every item you possess in any storage capacity you have access to that matches the search string. Then its right click the item in the chat window and use the "search for item" command and it gives you every location you have that item in on one screen(you would only have one of this mask, but if for instance you were looking for a potion instead you could find them all at once).