I don't think a duct for fresh outside air would help, would it? Certainly not in Ventura on a cold foggy night. You need to dry the air in the cabin, lower the dew point, not admit more humid air. It seems to me the easiest way to achieve defrosting would be to fix the air conditioning.
I've driven 6018 on cold foggy nights in Ventura, and for 6 hours in pouring rain, and never had a problem with window fogging. I just operated the air conditioning along with the heater or defroster. If I turned the A/C off for even a brief a moment the windows would start to fog-up.