Oh, no! Step back from the edge, crisc! I'm really sorry for your disappointing news!
Do you know any "smart kids" or where they go to school? Is there any sort of GT support group (PAGE, POGS, etc.) in the area? You could find out where the kids of the members went to K and see if there's a true peer there.
The Montessori school sounds like a known quantity, and while the teacher is clearly doing her best, bless her!, it doesn't sound like a good option to me. Running out of curriculum? No true peers? Not great.
The half-public-and-half-private option doubles your chances for finding a peer, and at least you know that the public K is trying to work with you, but it still seems like you're too likely to wind up with a bored child. This seems like a possible solution, but not the best ever.
Private K is a totally unknown quantity. I think you need more info about the private Ks if you're going to make an educated choice about this. What do you know about the private Ks in the area? What are your options?
Waiting for DYS notification in the hopes of advocacy help is very smart. Unfortunately, it sounds like you really need it, and right now!
I'm so sorry!
{{hugs}}