Is it bust, or completely missing?
IIRC they probably come in Metric or Imp., if there’s a preferred flavour…?
Is a drawing any use – might not be a huge/complex job to hog one out if worst comes to worst, I will assess later.
There’s an Ebay seller called ‘Heritage-lathes’ who deals in Hobbymat stuff and is a reasonable human being – might be worth messaging him..