Build a silo, then sell it. one civilian will appear.
Use the following procedure to sell the indicated buildings for free minigunners: For the GDI missions, sell a Guard Tower or Advanced Guard Tower. For the NOD missions, sell a SAM site or Obelisk Guard Tower (Obelisk of Light). First, select the "Sell" button in the Sidebar. Then, use the Left Mouse Button to sell the building. Use the Right Mouse Button to activate the selection cursor. Use the Left Mouse Button to select the building and press S. Note: This only works in versions earlier than v1.22p.