I think I just found them
They are called LUND COLDFRONT WINTER GRILLE INSERTS
Lund COLDFRONT WINTER GRILLE INSERTS - JCWhitney
But another sites indicates they are no longer made
Lund Grille Insert: Lund Grill, Lund Cold Front Winter Grille, Bolt Over Grill, Chevy Grill, Dodge Grill, Ford Grill, Truck Grill Cover
The last site seems to indicate these were only ever produced for trucks etc,
This site shows a good picture of them and you can see how the clips are constructed
http://www.autotrucktoys.com/chevy_s...e-PRD4187.aspx