Where to buy a vacuum unit

Been told that the vacuum unit on my distributor has broken and needs replacing however I can't find one for the correct engine size.  Car is a 1990 karmann clipper 1.8 petrol automatic. Thanks in advance

Wow, I thought that by 1990 all cabbies had Electronic ignition on the Dizz as in Hall Senders.  I personally have never seen a Vacuum unit on a 90-ish Cabby but then again I live across the pond.

I know over here it is very unusual to source a Vacuum assisted Klipper Cabby from 88-up, CIS or Digi.

When you say Petrol is that a Carbed car or Injected?

It's on a 1.8 petrol running on carb