The only mechanic I know in Galveston is Lazer Marine, located at GYB. Go by West Marine and pick up a boaters directory,,I'm sure you will find one in there.
On the West end you can use Troy's Marine or John Coleman. I've had both help me out a few times in the past and Troy actually walked me through fixing a emergency situation on the phone when he was out of town. They will both come to you and they both work on Yamahas. Unfortunately I don't have either number with me...try information. If you still can't find them send me a PM.
Finish Line Marine on Hwy 6 in Hitchcock. (4120 Hwy 6) 1 Mile West of I-45. Outstanding service on my Yamaha. 409-938-4408. Ask for Mike, Chris, or Chad.