H4 Stamping In third country

Me, Spouce and 2 kids had dropbox scheduled, at dropbox they denied document submission for my son who had turned 14. So now me, my spouse and younger son have stamped visa along with NIE approved, but can not travel back to usa since my elder son did not get stamping, We have been unsuccessfully trying for last many weeks to get a schedule for his appointment in India. Now since schools will be opening in a month and i also need to return due to professional commitment my only option is to try to get stamping for him in some third country.

Need help with what are my options. And can i use Schools opening (My son is in 10 th grade) and Family separation as we all have stamped visa except him as a ground for Emergency appointment. As i understand we can only apply emergency appointment once i get regular slot which is not happening in India.

Also has anyone been able to get H4 stamped in any third country recently.

Thanks in Advance.

What was the reason?