For ski, for wake, for skate
Hmm thats not good. Try ebay, or failing that you may have to contact a Yam dealer.
If its not written off the engine, I suggest you give it a full check over as it sounds like its never been properly maintained.
Oh dear, sounds like a bit of a nightmare for you.
You could alays have a look at another Fletcher up that way, its for sale on the sportsboat forum at a very sensible asking price and from the description has been well looked after, here is the link to the page
one of the Sportsboat Fourm members (whose Fletcher forum membership is still pending - so he cant post here yet) has suggested you take the boat into Stirlings Marine if near Lomond, he advises they are pretty good for Yam stuff.
I have use a chap who sells new and second hand part. Outboard spares unlimited 01622817073
Hope this helps