I had a traumatic injury a few years back where a piece of metal pierced my colon. Since then I cannot produce sperm. What can I do?

Urologist. You need evaluation by urologist or fertility specialist. If you do not produce anything with ejaculation (no semen), then your injury may have injured nerves controlling ejaculation. There are different techniques and procedures that may be performed to extract sperm.
No sperm? I think it unlikely that the trauma or surgery of the colon would prevent you from producing sperm. I agree that you need a urologist to determine the problem because there may be treatment to restore sperm in themejaculate. We can aspirate sperm from the testes while you are sedated and use the sperm for ivf by injecting a sperm into each egg from your partner. Get a diagnosis for options.