Dear Mr. Furman,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located Reports of Site Locations, 1837 - 1950 in the Records of the Post Office Department (Record Group 28). Records for New York County (aka Manhattan) are in the file New York: New York - Oneida that has been digitized and may be viewed online. However, the bulk of the documents from New York County are from the 20th century and we could not find any relating to Station A. For more information about Post Office Department records in National Archives custody, please email National Archives at Washington, DC - Textual Reference (RDT1) at Archives1reference@nara.gov.
Due to the COVID-19 pandemic and pursuant to guidance received from the Office of Management and Budget (OMB), NARA has adjusted its normal operations to balance the need of completing its mission-critical work while also adhering to the recommended social distancing for the safety of NARA staff. As a result of this re-prioritization of activities, you may experience a delay in receiving an initial acknowledgement as well as a substantive response to your reference request from RDT1. We apologize for this inconvenience and appreciate your understanding and patience.
According to the United States Postal Service, in 1659, an official repository for overseas mail was reportedly designated for New Amsterdam. The first post office in New York County formally established by the Continental Congress was that of Ebenezer Hazard. The article Stations and Branches states that “The earliest known Post Office branch was established in New York City on January 1, 1837, at the corner of William Street and Exchange Place” as a supplement to the main post office of the city, and it also references the “General Post-office in Nassau-street.”
Please see the following lists from the United States Postal Service of Research Sources and First Post Office Sources. You also may wish to contact the New York Public Library and the New York Municipal Archives. Also, New York Postal History: The Post Offices and First Postmasters from 1775 to 1980 by John L Kay and Chester M Smith may have the information you seek.
We hope this information is helpful. Best of luck with your research!