Concept art is the available only in Battalion Wars 2 or BWii. (突撃!!ファミコンウォーズVS, Totsugeki!! Famicom Wars VS).
An example is below with the Iron Legion's Battlestation.
To view Concept Art:Edit
You have to unlock it by obtaining S rank campaigns in the Story Mode.
Once obtained, you'll be able to view it in the "Extras" option within the game.