Older Vetus engines are marinised Peugeots.
Newer ones are marinised Mitsubishi Diesels.
Provided you have a Vetus model number for the engine you can probably find someone who will tell you what the base engine is. Then the parts will be compatible between the original engine and the marinised versions -- except for things like the raw water system, heat exchangers, etc.
Mine is a Vetus P.19 which is a marinised Pug XUD9. I've found a mob here called French Auto Spares who carry pretty much all of the parts for that, and also made notes of after-market equivalents for things like the oil filters, fuel filters, etc. I had a pre-filter at one point that was by Vetus but I've since replaced that with a Lucas/CAV so parts for that are easy to obtain (and much easier to fit). The original Hurth gearbox has also since been replaced with an up-specced hydraulic unit.
Good luck with your bright yellow unit, nice to see some other Vetus drivers about.