I've specced Yanmar diesel outboards on work boats for fish farms, etc, but recently have been told by the Yanmar dealers here that the diesel outboards are no longer really availble. I believe they were only ever batch built in response to someone like the Australian Government ordering a load at a time.
Although they found favour in some markets, they were horrendously expensive and heavy with only two (low-ish) power options.
I think the advent of the larger 4 stroke petrol OB's killed them off for most uses.