they don't advertise them on the Berettausa website but are listed on the international Beretta website. Look at the DT Double Trap model...it has one barrel as having Optima choke and the other barrel fixed.
http://www.beretta.com/Long-guns/Competition-guns/Over-and-Unders/DT10-X-Trap-Calcio-Montecarlo-Optima-Bore-Optima-Choke/index.aspx?m=82&f=2&id=136&did=1949