Ok i guess this has been asked before a million times or if not its something so obvious i should already know..!?
Is there any way to obtain LD cards at all or is it purely if you were Lucky enough to hold them prior to LD status??
There is only one way to obtain Ld cards and that is via completing their missions when they are available. However a card is created as an Ld meaning that a card cannot become an Ld as opposed to a card possibly becoming a CR.
You can see the missions required to win each ld card on this link: http://www.urban-rivals.com/en/missions/legendary/