James,

  I've recently had similar problems with a couple of mounts and what I did was 'phone around a coupe of local small engineering  firms. It only took me three calls.  The first was too busy but referred me to another who was at the time closed due to the virus, but is open again and can make piers.  The 3rd could do the job I wanted which was to make an adapter plate for a Paramount ME after which he was able to make the Owl nest adapter to hold the EQ8 to a metal pier, which funny enough I'm putting that  up today.  He is willing to take on other jobs for me.

So I'd phone around simple plans or photographs to work from is all that is usually required.

Good luck,

Eric

Have you  looked at the  web site of Rother Valley optics. under the listing  of  Mounts  their own  section under  Rother  valley  lists a mounting plate  at £125.00. .  Hope this  helps