First, download
Taliis DBC Editor.
After that, make sure you have Java. Now, open up Taliis and find Item.dbc to open in Taliis.
If you have it opened, here are the column names and information:
http://collab.kpsn.org/display/tc/Item.dbc+tc2
Right Click an Existing row -> Clone Row
After you cloned it, scroll all the way down to find your cloned row. Change the EntryId to your item's entry and the other information that relates to your newly cloned item.
Once you have everything you need do -> File -> Save As -> Item.dbc
First, copy your newly saved Item.dbc and paste it in YOUR_SERVER_SOURCE/dbc/ folder. You'll always need to do this so the server can read your new items in Item.dbc. Make sure to restart the server after replacing the old Item.dbc with your new.
Since you have that done, you need to create a patch. (Or you can create a folder in World of Warcraft/Data/ called patch-8.MPQ (patch-NUMBER THAT ISN'T TAKEN.MPQ))
Download
MPQEditor
Once you have that downloaded, follow the small guide below:
1. Click New MPQ
2. Name your MPQ file patch-NUMBER_THAT_ISN'T_TAKEN.MPQ, Example: patch-8.MPQ
3. Click Next
4. Select Create an Empty MPQ Archive. Click Next.
5. Size of hash table: Leave it alone. Click Next.
6. Select: Create an MPQ Archive with format version 2.0. Click Next.
7. Finish.
8. Create a new folder called DBFilesClient in the MPQEditor
9. Drag your newly edited Item.dbc inside of that folder.
10. Move your patch into World of Warcraft/Data/