In GTA Vice City, the weapon can be bought from Phil's Place after completing Phil Cassidy's missions. This is the only place that the weapon can be bought from. The weapon also has a slow firing rate, making it a poor choice of a weapon to use. However, it is powerful as the player can kill a person in a single shot, reguardless if the target is wearing body armor or not.
In both GTA Vice City and GTA Liberty City Stories, the weapon appears to be named as the M60E1. The bipod is folded and the bullet bow isn't inserted. Instead, a bullet belt hangs down from the gun.
GTA Vice City