This news has been retracted. I apologize for the misinformation. I misread the news and saw Drama CD as OVA. Therefore, there is no OVA.
Amazon Japan lists that Nobunaga Concerto
volume 11 will bundle an OVA titled "Shuugaku Ryokou IN Kyoto-hen." It will be released on September 12, 2014.
The manga's anime adaptation
is currently airing.