Mine is definitely plaster, and they were being sold here in Australia, along with the reproduction Trademark machines, in early 1984, which is when I was first offered a machine plus Nipper by a collector who was selling off his collection due to devorce.
If I remember correctly it was George Paul who once posted here that the machines with a soundbox serial number J18425 were a Japanese made reproduction, so I assumed that the plaster Nipper that was always sold with the machines originally, also came from Japan.
Perhaps the mould for the late 80's resin Nippers made by Mr.Taylor was taken from one of the plaster statues?