You mean like this?
http://www.mcnichols.com/products/perforated/hexagonalhole/
These guys have a lot of different types of metal. Sometimes, if your not needing a whole lot, they have what they call 'off-fall' (I think that's what they called it) it's what's left over on the floor when they sheer off bigger jobs. For a grill opening, of a lower valance opening, this would likely be the best sized piece to be able to get and they sell it pretty cheap if it's 'off-fall' too.