I don't know much about car parts suppliers but anyone who sells K & N filters should be able to set you up with some thing. I think they call theirs the PreCharger.

Any of the online bike parts places will have PC Racing Filter Skins. They're made to fit bike filters but check the sizes and you might find something that will work. Try http://www.denniskirk.com

Or you can get one custom made to fit your filter from Outerwears at http://www.outerwearsracing.com/custom_order.php