As said, take your documents to Ford and they will charge you around £50 for a new plate. The actual plate is around £3, but the rest is for them to send docs away to DVLA, they stamp one up and send it back to Ford for you to pick up.

You could get one of the aftermarket shiny vin stampers to do one, but if you come to sell the car I'd say most people would ask to see the original as well. Plus I think even those are around the £25/£30 mark.