Amazon with YEHANLY has the YEHANLY 5.1" x 11.3" Magnetic Vent Covers with Vent Screen (Black or White) for $24 - $12 off with coupon code Y8VL9JWL (click to activate) = $12 with free shipping on $35+ or with Prime.

Also available in Black 7" x 13" size for $15 after code Y8VL9JWL.