When you create a redistricting plan, the district layer is stored in the same location as the plan.
In this example, my plan “Enacted Congress B-BG-T-C” is saved to “C:\VA Data 2010 Final\Enacted Congress B-BG-T-C.rdp”.
The district layer for that plan is saved as C:\VA Data 2010 Final\Enacted Congress B-BG-T-C.dbd.