They are listed under two different identifiers on DVLA (search for coupe volumex and for VX coupe)and as always with old cars the summer figure is always the most reliable indicator.
Quarter 2 of 2016 is probably the most reliable published info (I think they haven't published this quarter for 2017 yet) as most cars would be in use at that period the total comes to 10 on road 35 sorn.