What do you mean?
They sell generic grill covers at any hardware, home improvement center or discount store like Wal-Mart, Target, etc. Or you can just purchase a plastic tarp and hold it together with bungee cords.
Buy a grill cover?
Is this an outdoor grill?
You can buy a grill cover from many stores or Amazon, usually they are enclosed when you buy a grill.
For the diy'er in you:
hometalk has this idea!
We just have a black grill cover. Ours came with it. Could you look up your brand and order one? Amazno usually has generic cheaper versions too!