This supplement of Memoir '44 offers experienced players the unique opportunity to replay historical WWII battles on a grand scale, with up to four players to a side.
This style of play, called Memoir '44 Overlord, combines multiple board maps into a single, oversized battlefield. To play it requires this free downloadable game supplement, and at least two copies of the game.
With Memoir '44 Overlord, players can experience the frustrations associated with being part of a military-style WWII chain of command and, at the same time, enjoy the challenges of coordination and cooperation needed to gain victory.
From the description... Bold emphazise is mine.
So just a downloadable free pdf that required you to have 2 boxes of memoir 44, this is not something that was sold.