The MD2B was a great engine. I understand they are one of the hardest and expensive to work
on though. I've also seen quite a few that are salt water
cooled. Maybe that was your issue? I forget the details as my last one was 25 years ago! Craig's list is a good resource. Unless an MD2B drops in your lap it might be worth the trouble to change to a more recent model; universal, kubota etc.
the other option is to pick up a 10 hp outboard
and bracket, either for until you find the perfect engine deal, or permanently if you're not sailing off long term cruising