The tool should have come with the gun (assuming you bought it new).

If you call Knight using the number in the owners manual they may send you a tool at no charge if it was missing when you bought the gun.

They were great when I called about a missing c-tool (used to clean the bolt on a DISC rifle) that was missing when I opened the box. They sent me one as soon as they received my warranty card. Also, they were great to talk to in general about the gun, loads, cleaning, etc.