So....how did Dr. Brantley and the nurse get it?
The ZMapp monoclonal antibody existed in a very small batch. It was intended for testing on primates. A big exemption was granted to extract Brantley and Wrightbol. I suspect the private investors ponied up money to rescue them as a proof of concept. Success would bring great publicity. It's not a substance that can be manufactured rapidly or in large batches. The worst case is they die anyway. Best case is a successful publicity stunt. They got the latter.