I've used Brad at Fiberglass Atlanta for a few small gelcoat repairs and some wet sanding / clean-up stuff. He does high-quality stuff and was very reasonable.
Brad works out of his house out west of town near Douglasville. A bit of a haul for us north-siders, but it was worth the drive.
He usually is pretty backed up, but if you talk with him, you can work out the scheduling....especially if it's during the off-season.