I'm sorry. Would the teachers and principal be willing to talk to your family consultant or a gt psychologist, who could explain them that boredom can cause lots of behavioral issues and that not allowing him to accelerate to the 2nd will make things much worse? Have they considered how would that make him feel? If they are worried about his emotional needs then they need to think really hard what kind of message he will get from staying in the 1st grade.
I'm sorry the gt school will not open. DS was in Montessori before, right? Do they also have 1st-3rd classroom? I know the situation wasn't optimal and we weren't happy with our Montessori but it may still work better than the PS would.
Is homeschooling an option? I know that you really like your work but would it be possible to work p/t? Do you have any local private schools which carter to homeschoolers?