According to Amazon Japan, the 44th volume of the Diamond no Ace
manga will bundle an original OVA. This OVA will be an adaptation of the one-shot Kuramochi Youichi Special Bangaihen: OutRun
which is a part of the Diamond no Ace: Guide Book. It covers the "moving story of the Kominato brothers" which isn't covered by the television series.
Source: Amazon Japan
Diamond no Ace OVA