How to randomly loop an object?

Hi,
I have a helicopter that starts off screen and moves across, but the game isn’t very fun if more helicopters don’t come for the player to shoot at. Can someone please give me help on code for my helicopter movement script that allows more helicopters to come from a point off-screen and keep looping? It’s a 2D game if you haven’t guessed.
Thanks!
Gabriel

public float scrollSpeed;
public float tileSizeX;
private Vector3 startPosition;

 void Start ()
 {
 startPosition = transform.position;
 }
 void Update ()
 {
 float newPosition = Mathf.Repeat(Time.time*scrollSpeed,tileSizeX);
 transform.position = startPosition + Vector3.right*newPosition;
 }

You can add this to your game object and change the values according to your requirement.