What now?? :(

Im searching for any of my husbands birth family.. so far we have some non ID info, the agency he was adopted through, the hospital, what his birthmother named him (first name), and we found through the birth index his birthmothers maiden name(last name only). Now, Im stuck.. I dont know what to do next or how to do it... How can I request birth records? I dont even know her first name.. How can I get a copy of his original birth certificate- they want proof of who you are... I feel like I am at a standstill.. does anyone have any ideas... He was born and adopted in New York City. DOB 8/21/71 Thanks :confused: