Can I replace just the plastic frame around the glass panes on my front door?
If you look on the hinge side of the door you may find a makers tag with a model number. If the door is fairly new the manufacturer may be able to supply a new one. You also might try a glass and window shop. The grid is typically screwed to the door. Small plastic plugs cover the screw heads. Some that I have encountered also have an adhesive applied. Sliding a putty knife under the grid will release the trim.