I'm suprised no one reffered you to me, (as being the resident Boat expert
You can get a Borg Wagner trannsmission from almost any boat motor dealer. Also you must remeber to think about the changes in the fresh water cooling system and other such modifications you must do. I have seen a add in Boating magazine advertising trannies , here's the places phone number its in Mass (I've never been there I'm on Long Island)however a friend of mine ordered a engine from them and got great service (508) 791-4917. I have a 27 foot Grady White with twin Mercruisers. What about you ?