Hi Ian, I had similar aspirations but small veg vans are getting thin on the ground and I ended up with a 56 Peugeot Expert which is DW8 and Lucas that I'm hoping to convert to Bosch.
Other than French offerings, VAG 1.9sdi will run veg but it seems that many Caddys have the wrong pump and Isuzu engined Vauxhall's but they are fairly rare now.
You might be better off finding an estate or using bio which will open up many more options.