I had spare keys for my 'Cuda cut at the local Lowes store. The kid behind the counter looked at me funny and says "how old is this key?!" "about 45 years old or so" :p He searched, but found no blanks in the older chrysler style. So i had him cut me a Door/Ignition Key from a newer Chrysler blank (single sided style with the big head on the end, the kind they used in the 80's Cars & Vans)
"I dunno if this will work, man...it doesn't look like your old key" :p I wasn't worried about the fact that it wasn't a "pentastar" shaped key, since the ignition is in the dash. Sure enough it works perfectly.
Then i stopped by a local hardware store, to get a spare key cut for my '48 Dodge Truck, and it turns out they have the older "pentastar" Chrysler keys in stock. So i got them to cut me some spares for my '74 Duster (which i was driving that day) while i was there. The key for my '48 was a little more difficult, they had to use a weird Ford Blank and it took 4 different tries/blanks before they could get one cut close to it (and then i spent an hour at home fine-tuning the shape of the key with files, sandpaper and so forth)