There is a chain out here in California called TAP Plastics,(they have retail stores) they can make you a custom cover for around $80.00-$90.00 depending on size (apprx. 19" x 15" x 5") and thickness (1/8" or 1/4"). If there's one in your area check 'em out.
ps. I have no affliation with them.
ps. I have no affliation with them.