These are old NAGS #S (National Auto Glass)
The #s I believe are the same but the prefixes have changed , most glass shops can interchange these #s
59-64 W678
65-70 W761
71-76 W788
You can also try Pilkington Glass. They routinely make the procar windshields for that era from original manufacturing equipment.
Try
www.Glasssearch.com www.pilkingtonclassics.com or 1-800-848-1351.
The windshield is the same from 59-64 CC ( Ambulance's , Hearses, Flower Cars) and 59-65 Limousines I do not think Pilkington Glass has any of the 59-65 in stock or making any at the moment , but you will need to contact them and ask. Might be other sources to try but this is the only one I have dealt with. 59-60 other Caddy's look similar but are to short , the CC ( Commercial Chassis and Limousine windshields are a few inches taller) Do not let someone try to sell you a 59-60 windshield from a different model other than one that fits a 59-64 CC or 59-65 limousine.