I have a friend that has a '68 Mustang and got some unused '68 plates that have "Hemisphere '68" and was able to use and registrar them on his Mustang.
If the plates are old you might could sell them to vintage vehicle owners.
They are all from the 60's and all kinds car, truck, farm truck, tractor. short trailer, long trailer, bus. My mom and dad bought a house in Eastland in the 70's. There was a old falling down shed on the property and I got to digging around one day and in the back were a lot of boxes with plates with tissue paper between them. Turns out that the lady who owned the property and had passed was the county tax assessor for 4 years and any plates that were not issued were stacked in the shed and it fell down around them