I would say that depends a bit on the damage. A couple of theeth and/or tips of the cogs, it would be ok to weld up and grind to shape. Carefully done it would be passable as there is quite big gaps and not particular stringent mesh between the two gears. A good pro welder could recommend the right welding rods or material to use for the right hardness. If the cogs are too far gone, it would be a matter of finding a cog segment to replace the old with. Original the first cog on the segment is ground to half, to make it easier to mesh in with the motor gear.

I would be surprised if there wasn't a standard gear to find that could be used, gearcogs are pretty standardised.

Tom, what rod did you use?  1/8" 6011 breaks right off when I try to kickstart

Kieth Fenner, on U-Tube has several good videos on repairing damaged or missing gear teeth with brazing build up and machining.   

Here is an idea for repairing your damaged gear. Cut off the damaged section and graft on a new section from a compatible gear.  Probably need to braze as arc welding will crystalize the parts.