Even though a Nissan dealer may not have the vehicle you want. As long as you've test driven the same model, maybe in a different color, that dealer can buy the vehicle you want at the other Nissan dealership and sell it back to you. It shouldn't be at any extra cost. Don't expect them to give the car away below invoice though. Locating/swapping cars aren't cheap.
We do that all the time for several reasons. A customer knows they can get the car elsewhere, but the customer knows how honest and friendly of a dealership we are so they rather do business with us. OR, the customer has us locate a vehicle because the one they want is just too far away.