There are several Eisenstadt families in the NYC records at the turn of the [20th] century. Most are in New York County, which is Manhattan, but you should also try Brooklyn and Queens. I have Eisenstadt relatives who came before 1900. I found a birth record of my great-aunt under Izenstock! the NYC Archives will do a search for you also. It is located at 30 Chambers Street, 10007.