I have repaired large chips in my cork grips with wine bottle corks. I ground out the defect using a drum sander attachment in my drill press (diameter sized to match the wine cork, slightly smaller works best.) I sliced the cork in half so I had a flat surface on one side and glued the repair in place using Titebond II and a light spring clamp.

When the glue had set I carefully trimmed the excess with an exacto knife and hand sanded the patch to match the surrounding surface. The repair is slightly visible since the grain on the patch runs in a different direction than the grain in the handle. I was more concerned about the 'feel' , the damaged area was just under my thumb and would often give me a blister.

For a less visible repair use a cork ring cut into a triangular wedge, the sloping sides help fill any gaps as clamp pressure is applied.