As a former PY23 owner I'll chime in here.
The PY23 is a great 23 footer! IMHO it's a nice-looking and nice handling boat that's easy to sail and great to learn on with an interior layout as nice or nicer than other similar mass production boats of that size.
Paceship yachts sold the line to AMF in the mid-to-late 70's and AMF only manufactured for a few years after that. The PY26 molds went to tanzer and the PY23 went nowhere.
I know of no company selling keels or model-specific parts for the PY23.
That said, if the rest of the boat is in really nice shape and the price is really right I guess you could consider buying it and refurbishing or refabricating the swing keel if you're looking for and have the skills for a project and have the setup to drop and reinstall the keel. However, that will be no small task. Walking away (make that running away) should be seriously considered.
There are a lot of PY23's out there at attractive prices. I think they made at least 400 or 500 of them over a 6 or 7 year period beginning in about 1973 0r 1974. I think the last year AMF produced them was 80 or 81.
Check out yachtworld, sailboat listings.com, sailing texas, etc.
But above all check out the Paceship website: The Paceship Website Homepage
It's the definitive source for all things Paceship, including downloads of the PY23 manual and a classified section where you can find paceship boats, parts and accessories for sale.
1973 Paceship Chance 32/28 "Westwind"