If you can not find the windows and are not a purest, they can be made easily by using clear plastic sheeting from toy boxes, file paper covers, etc. Cut them oversize to allow material to clear glue (E6000 is one) them to wall.
Use Marks-a-lot or Sharpie colored markers to add colors and design as wanted. They will show up great if you install a light in the ceiling of the church.
Charlie