I think Boatworks in South Windsor does fiberglass repair. I replaced a transom on an old 15ft lake boat I had. It wasn't too bad. You just don't want to touch the outside fiberglass and do everything from the inside. It was tough to get the cut out pieces to line up well with the existing pieces, but is was an old boat. But, it worked.
Once it was finished, the boat did run better, until is sunk
, but that is another story.