Where are the D.C. Duplexes?

[Matt Vaughn]

So what does a guy have to do to find a duplex around Washington D.C. these days? I'm looking for our first home, which I'm also intending to be our first investment property. While my first preference would be a duplex (so I can learn how to landlord), I hardly find 5 duplexes on the MLS in the entire DC, Maryland, Virginia area (excluding SE D.C.).

Are duplexes not usually listed on the MLS? Are there better ways to find them? Once in a while I see a SFH with an accessory basement apartment, but I understand that I'm not supposed to rent both units if I'm no longer an occupant. Is that rule enforced?

Interested in your thoughts.