What treatment is available for very freguent and very odorous gas it is so bad I cancel appts so as not to be embarrased?

Probiotics. Try probiotics - particularly tract star from probioticsmd - they work great.
Flatulence. If this is not your norm, a plausible diagnosis could be giardiasis. A stool sample would identify the problem and Metronidazole would treat it. Seek medical care to also rule out lifestyle or meds as the culprits.