You don't say where you're located, but check the local papers and on line for car shows in your area. I got my 1956 truck plate at a car show at the NC State Fair Grounds in Raleigh a couple of years ago and picked up a Raleigh city plate this year.
Watch out that you get a truck plate and not a car plate. In North Carolina they are different. Car plates start off with 2 or 3 letters and then a dot and 2 or 3 numbers. Truck plates start with numbers and then the letters. City plates don't seem to matter. Usually, you can get the plate you want cheaper at a car show than on line, plus you can see what you are getting up close.
I was going to,get a YOM plate for my recently purchased '71 C-10, but I found one under the seat!
Best of luck in your search!
best wishes,
Les
