You can get the alternator at any auto store
Compare yours to the new one closely
They have to be the same in every way looking at it
The alternators output could be a bit higher than stock but all good
The store will check your charging system on instruments to see it the problem is the alternator
A very good idea is to clean to shinny metal the connection of the negative battery terminal to the frame of the car that is located under the battery tray
Do the cleaning before you go to the store
if you find the regulator to be the problem ( at the store ) I would clean all electrical connections and ground connection of it and a very good chance it will come back to life from prior experience on here
David, I have been running & Selling the AutoZone sourced DL7122 rebuilt alternator for over 2 decades with excellent results. It is rated at 55 amps which matches the max amperage used on the 63/64 Cadillac alternators, and more importantly is a direct fit piece... just remove the old and install the new. I buy in batch when I can get a good deal on them and have 2 on hand right now. They are $45 each. I checked and are currently $61.99 + $15 core charge. So I have them discounted over $30! Depending on when I have bought them they come with gold or black fan blades and currently have one if each. See below. If interested shoot me an email with shipping address to email@example.com.
New Rebuilt Duralast 7122 55 amp Alternators - $45 each
I have a couple of new rebuilt AutoZone sourced Duralast DL7122 55 amp direct replacement alternators for $45 each. Email me at firstname.lastname@example.org.