L..
Did you talk to someone in medical records? If they don't have it, many times older records are sent to storage facilities off the campus. Maybe ask about that?
I'd be surprised if your old OB didn't have it. Maybe you could try the pediatrician? Could be in the birth record of your first child's chart.
Otherwise, I'm not really sure. Medical records can be a pain to track down or get responses about. Good luck!