Solution.
1. Go to WoWhead, in every link you will find an EntryID for the item.
2. Convert your Item.dbc file in your dbc/ folder to Item.dbc.svc with a program called DBCutils.
3. Using a program like Notepad++ Ctrl+f through the svc using the EntryID, if a row begins with that entryID, the other large number on the same row is the displayID.
Also the TrinityCreator automates this process substantially, linking to the dbc and allowing a search functionality.