APPLIES ONLY TO XR (Brief bit on Scorpio at end): OEM: There are a couple of OEM key blanks available. They are manufactured by ILCO and the key blanks are TX and TXY (maybe another too). They are manuf. in Germany. Not sure of the difference in TX and TXY (mine are all TX's), but the ILCO rep (I think this is what he said, this was like 2-3 years ago) said it had to do with the key stop(correct term?) . The key stop correctly positions the depth of the key when inserted.
WORD OF NOTE/CAUTION about the OEM ILCO blanks. They are steel. Locksmiths will not touch them with a 10 foot pole. Merkur dealerships were apparently provided a cutter to cut these blanks. When I lived in Gainesville, FL, Prestige Lincoln-Mercury-Merkur let there key cutter go with a mechanic (ARGH!), so I had to drive to Jacksonville to get them cut.
AFTERMARKET: The key blanks for XR door/ignition are readily available at many places, though they are unfortunately becoming much more scarce. Though I'm finding it much more difficult to find any generic key cutters that carry blanks, any locksmith should. As far as going to generic key cutters, this same blank was used for 77-80 Fiesta's and 70-77 Capri (potentially useful info for lookup when you get, 'a Mer-what?').
Better yet, here is some aftermarket key blank info (for XR's): Manuf: Taylor, Blank : X86 (probably most common blank available) Manuf: Taylor, Blank: X20 (smaller key head than X86, great for keeping in wallet, head too small for daily usage unless you've got strong fingers) Manuf: Taylor, Blank: T81 (This one will work but the key stop is not as wide, could be a troublesome blank for an XR). Manuf: Curtis, Blank: FC-7 (basically the same as Taylor X86) Manuf:Cole, Blank: H7 (basically the same as Taylor X20)
REALLY DESPARATE? : Volvo key blank that is easily modified (remove some ridges in the key stop area): Key grooves otherwise similar enough to work, though a bit tight. Manuf: Cole, Blank: Three diff. #'s on key: X30,VL4,V073S
SCORPIO: Scorpio key blanks are a different beast entirely, two different types of special security blanks, also manuf. by ILCO if I'm not mistaken. Special key cutters and all. I have no experience with these keys so I will comment no further.
Ever notice that your original XR keys don't turn yellow after years of usage (no nickel to wear off, no brass to show)? As far as I know the OEM keys are still available though I imagine they are rather expensive. Contacting ILCO may yield leads on getting the OEM TX's if you want them (These have the plastic head with the Merkur emblem molded into it). Big advantage to steel is that they basically never wear out. Some have said they're hard on locks, but the 70's Capri used the same steel OEM blanks and I have yet to see one of them with worn out locks.