I was wondering what are some good alternatives for diabetes-based foot gangrene if the weak ointment that the doctor gives isn't working?

Requires debridemt: Gangrene cannot be treated with ointment. It requires careful removal of dead tissues (debridement) to get to areas with circulation. Important to use leg elevation, compressive stockings, etc in order to reduce leg edema (swelling) which worsens circulation needed to heal. Some are using biocellular injection treatments along with surgery to improve blood supply and healing ability. Reduces recur.

Have it re-evaluated: Gangrene is usually sign of significant compromise to the circulation with or without and infection. You may benefit by seeing a vascular specialist to address the circulation. Without adequate blood flow you may not be able to heal no matter what kind of ointment you are applying.