In reality, you're probably going to have to rebuild them, NOS or not. The gaskets and seals will be shot after 40 years. Most used ones will have a problem with the electrical switch.
I'm in the process of doing all of this right now. You can buy non-functioning pumps on ebay for sub $100, but will then have to rebuild them. Gaskts are about $90, a new filter is about $30, and then there is plating if you need that, too.
Andrew Booth (Charley Farley) on this site is a wealth of knowlege, and has the parts you'll need. Do a quick search, and you'll get what you need. I suppose if you are so inclined, Andrew can rebuild them for you.
Good Luck
