If you go to the Facebook 'Bukh Marine Diesel Owners Group', er, group, there is at least one person/firm in India (presumably dismantling lifeboats) frequently posting to offer second-hand Bukh spares. (One called something similar to Marine Enterprises.) I have never used them (yet!), but have seen posts from people claiming to have bought from them and been very satisfied with the spares and the speed of delivery from India.
You can also sometimes find odd bits on eBay and Facebook marketplace.
Most Bukh spares are still available new (some DV series engines still in production), but tend to be expensive (a few outrageously so).
What in particular are you after?
Here's one of the Indian second-hand Bukh engines and spares traders on the Facebook group (also contactable by Whatsapp, I see):
Just came across this company I've not heard of before, also on the Facebook Bukh group. Based in Weymouth - is this a re-incarnation of Marine Enterprises. A chap named Sean involved. Do I recall reading that name somewhere as being either the new or previous owner of Marine Enterprises?