When I bought my M1A new in the box, it came with a copy of Department of the Army Technical Manual ,TM 9-1005-223-12, Operator and Organizational Maintenance Manual, 7.62-MM Rifle M-14 and Rifle Bipod M2.
It is a good manual. although for the M-14, it applies to the M1A as well.
If your Dad bought it new it should have came with one. Call Springfield and they should be able to supply him with one.