A cooperative US dealer's parts dept. manager MAY be able to order them, but some European parts (usually special performance parts) are not allowed in the US through normal dealer's channels. This should not apply to plastic body parts, but who knows?
Alternately, you might contact one of the many UK or European Forum Members here and ask for a recommendation of a good dealership to contact for a direct purchase.
Finally, you could ask if any European Forum member might want to trade their black grills for your shiny chrome ones and work a swap.
Each side of the grill is independent, so you can also just switch one and have a truly unique X3.
