My father used to say: 'thems as asks may not get, but thems as don't ask, don't want". Sometimes it's worth being a bit cheeky. If I were you, I would use the form on the membership list to email any member who has the sort of boat you want. (This will show the email as coming via the JRA, so the recipient will know it's kosher.)
There are quite a few boats that aren't 'seriously for sale', but might be if someone is offering a fair price ...
And of course there is the delightful Emmeline in Holland.