n December 2016 Ebay seller juraantiq from Latvia was selling replica Soviet Union plates. He is selling them as replicas (which is good).
They are being made to order in Ukraine after you state what registration you want. The plates seem fairly accurate but the big problem is that the pre-made mounting holes are not there.
Although USSR (CCCP) plates from this period are not very difficult to get it will be necessary to check carefully any you are offered or want to buy to make sure they are genuine.