I know of a few by me...one is semi-retired only taking on jobs he wants...did a heck of a job on a tear in my canvas covers and was cheap. McAuley Canvas in Medina NY. Like I said though, he's semi retired and only taking on jobs he wants to do which may/may not be your boat.
There's another that is adjacent to a used car shop and constantly has different boats of all sizes and classic cars parked outside so must be doing something right. Dave's Trim in Lockport NY.
There are others through either FB Marketplace or Craigslist advertising boat upholstery. Or check with your local marina as I'm sure they have an idea of who to reach out to.