The statues required to unlock the Solar Gun can be found at the following locations:
STATUE - LOCATION Crying Wolf - At Stage 4: Shadow Moses, behind Snake's starting spot in the human phase of the Boss fight. Frog Soldier - At Stage 1: Middle East, Advent Palace garage, atop the Nomad vehicle. Laughing Octopus - At Stage 2: South America, in the Research Lab Boss room, upper right room. Raging Raven - At Stage 3: Europe, on the top floor of the human phase of the Boss fight. Screaming Mantis - At Stage 5: Outer Heaven, near the northern-most door during the human phase of the fight.