I don't think this list has the POH for the P model, but it's got other information that might interest you.
In my opinion, just as important to study as the flight manual, is the maintenance manual, particularly for an understanding of systems.
The 172 is a dirt simple airplane, but there's still good information to be had from the mx manual.
The site listed here does have a 1959 Cessna 172 manual...not nearly as complete as what you're looking for, but it's something.
The other poster is correct, however...an internet search will help you find what you're after.
Cessna FREE Manuals