A casual search shows a whole lot of Fords use a very similar, if not the identical, blank.... '88-95 T-birds, '81-87 Escort, F150's, F250's and probably many more. Even Yamaha uses a similar blank....
One thing about the Marks is the trunk/glove-box/console is a mirror image of the ignition/door key.
Ebay had some Mark blanks at one time. Note that earlier '80s Marks used short keys which won't work, and a seller might not know or care. I think there are 3 possible lengths in total.
One online site sells a set of 2 'star' Mark VII blanks for $25. Maybe that price indicates they are difficult to find.
I once had a set from an insurance company. It was a wallet card thing with 2 plastic punch-out keys for emergencies.... I used it once. Probably still around here somewhere.. No clue how they molded them unless the digital pattern is available.