Fellowes Shredder Parent Part # 38605

If this unit is worth it to you, you can build your own gear.
Here is a link to get plastic repair materials to make plastic parts. This site also will have materials for repairing plastics.

Another possibility is to search Ebay for a unit like yours which has other problems. Never can tell... it may be there.
Make sure you ask for the model of the unit in your search (on the NET as well. The serial in this case is not needed.