In our current rental market it may be hard to find a duplex that has two vacancies at the same time. I don't currently see ANY duplexes (even just one level) available for rent in the MLS. You may have better luck looking for two condos in the same building or two townhouses in the same community. Good luck with your search!
Are you looking for two separate living areas as well as two kitchens? If so, this would be considered a duplex. There are a number of them located around Arlington and I would be happy to show you a few.