In all fairness, Don't bother to call Airstream , unless you just happened to pull up in front of the Jackson Center, Ohio, facility. They will just refer you to one of their national dealers.
The two links given here are good for the vent cover replacement. Check and make sure your original hardware is in good shape or, order it from Andy..I ordered mine from him and, it was a perfect fit and, quality was excellent~! pricey but..
Also, be sure to get the foam seal for the inside lip edge..(this seals the road dust, bugs, etc out..) Andy is also a great source for this or, you might try Lowes as well..
Take your time and, you should be able to get it done with no problems..
Also, may I suggest, use Stainless Steel hardwares..