I have an M1A SOCOM, which is a very similar gun.
I have an aimpoint 2x red dot scope on mine. However, I can tell you that people are usually very picky about their scopes. A standard variable power scope such as a 3-9 is completely different from a red dot scope. An m1a is a very nice, very expensive rifle, and he is unlikely to mount a scope on it if the scope is not exactly what he wants.
You may want to get him some spare magazines (or clips as some people call them, they hold bullets) rather than a scope. Or you can just find out what kind of ammo he has, and buy him some boxes of ammo. If you do get a scope, save the receipt and don't be offended if it isn't exactly what he wants on his rifle.