I made mine up myself in-situ. I cut a thin slice off a mastic tube about the thickness of the grommet. cut it so it opens up around the mentioned grommet, kept to size with a cable tie, and kept in place with masking tape. Then fill with black mastic, smooth out and leave overnight. Remove the next day and you have a nice new grommet covering the old on without all the hassle.
Easy.
