I have all the information needed to make this scenario (and a Roundup to Berlin scenario) at my house and at a close library, and other similar scenarios could expediate the process. Indeed, I am playing TOAWIII right now and began to start making a scenario, but the horrible interface of the editor was just too much time...
There is a scenario that lets one choose the beachhead, but it covers the entire Western Allied area.
To the above comments, look at the map! (Note also that the German division in the Channel Islands was able to quickly reinforce, and that there was a German parachute unit in the Cotentin peninsula, a regiment I think). There are no panzer reserves to counterattack on the first day at Calais. The beach defenses are stronger, but not notably stronger then Omaha (no cliffs at Calais), and the British had the equipment to deal with strong defenses.
There are fewer natural terrain obstructions in the Calais area in Normandy, so that means fewer bridges for the paratroopers and glider infantry to seize. Perhaps they could have attacked the coastal defenses from the rear? Paratroopers are lightly armed, but so are the German units at Calais (though there might be a handful of StuGs - assault guns). It might make the landings easier, but I am unsure of the specifics of this method, or if was even considered.
Another thing I forgot: the Germans flooded a large marshy area in the Cotentin peninsula, confining the Allied advance.
Look at these sites:
http://www.army.mil/cmh-pg/brochures...dy/nor-pam.htm
http://www.militaryhistoryonline.com...l/efforts.aspx
The Germans started out thinking that Calais was the main area (though some Germans, such as Hitler and Rommel thought it would be Normandy). The deception operation strongly reinforced this belief.
However, if the deception opration was targeted at Normandy instead of Calais, then the Germans would probably have put somewhat less forces at Calais, and somewhat more at Normandy, unless you think the the histroical deception operation did absolutely nothing in convincing the Germans to put their assets at Calais.