reproducing the cross

Where is the original cross? Walter Benjamin's "The Work of Art in the Age of mechanical Reproduction" raises this question for me. There are many reproductions of the cross but the original is, correct me if I'm wrong, no where to be found. The True Cross, the one Jesus was nailed to, was allegedly found in pieces during during the Byzantine era. Constantine the emperor is responsible for the reproduction of the cross, the image of it becoming popular during his time. But what does it say if there is no original?
Benjamin says that "The presence of the original is the prerequisite of the concept of authenticity," but there is not a true cross to measure this authenticity against (Benjamin 1234). This is not to say that there is no true cross, it is just that no true cross has been discovered in its complete form. So, what is being reproduced? The crosses from Byzantine? Crucifixes from medieval times? There are so many variations of these reproduced crosses out there, ranging from the massive monument at the Valley of the Fallen in Spain to the mock rosary necklaces sold in Rue 21. Would the cross at the Valley of the Fallen be considered an original? Obviously, the mock-rosary necklaces are reproductions, but what exactly are they a reproduction of? Which model of the cross do they use? Since there are so many variations, could it be that these reproductions are actually not reproductions of the original at all but reproductions of the wide range of imaginative ways of constructing the cross?