Your car being an LE "should" have a black grille bar as standard, has it been involved in an accident, or the grille been stolen at any point, I'm 99.9% certain a black grille bar is standard on the LE.
Your best bet is probably the main Vauxhall dealer as its too new a car to get one from anywhere else like a breakers, any Corsa Es you do find breaking will likely have front end damage, so grille will be useless, i believe they are easy to break when removing as well due to fragile clips, and any I've seen on eBay, even brand new from Vauxhall dealers selling on eBay have been advertised at overinflated prices. However were it my car I'd be looking to find out why it's not got something fitted that it should've came with.
EDIT: 64 plate? Is it a D or an E youve got, just realised i saw a red 64 plate D LE yesterday, without a black grille bar, Ds didn't come with one on any spec so it will need to be painted by a bodyshop.