Try e-gunparts.com. A good gunsmith can make one.
Standard Catalog of Smith and Wesson.
email the serial# to smith & Wesson and they will respond with the date
Standard Catalog of Smith and Wesson, 3rd ed by Supca and Nahas
Standard Catalog of Smith and Wesson, 3rd Edition.
You will have to find a copy of The Standard Catalog of Smith and Wesson and check each model number.
Try ask.com if you haven't already.
You can get it lettered by S&W.
You will have to call S&W and give them the serial number to find out.
Inside the crane or on the slide
You will have to call S&W with the sn to find out.
Contact S&W or get a copy of Standard Catalog of Smith and Wesson by Supica and Nahas.
You will need to find a gunsmith