You may consider contacting the American Institute of Architects.
The architectural firms may have archives: Benjamin Wistar Morris, architect; Carrere & Hastings, consulting architects, the AIA would probably know if they do.
The New York Landmarks Conservancy could be of some help, The Preservation League of New York State, New York State Historic Preservation Office, The Museum of the City of New York...
Plus, the AIA may be able to point you in the direction of the general contractor, whose archives, if any, would surely have a record of the clocks.