Our good fortune, for a change, the one thing that Airstream didn't custom make is the sink and lav faucets. Visit your neighborhood homecenter and spend as little or as much as you can afford. They are US plumbing standard drilled holes.
If your lav is a combo shower/faucet fixture, you might have to go to a marine or RV supplier. They will have a larger selection of this type of combo fixture.
-"You want to make it two inches - or, if you're working in centimeters, make sure it's enough centimeters for two inches."-Red Green