Not mine but I spotted this and it seems there's always someone looking for the M bumper grills.
http://www.ebay.fr/itm/Original-BMW-Z4-M-3-2-Liter-E85-E86-Gitter-vorne-7895842-/351665902880?fits=Make%3ABMW&hash=item51e0ebd520:g:hvUAAOSwnDxUcLuW
http://www.ebay.fr/itm/Original-BMW-Z4-M-3-2-Liter-E85-E86-Gitter-vorne-7895842-/351665902880?fits=Make%3ABMW&hash=item51e0ebd520:g:hvUAAOSwnDxUcLuW