Re: duck twin rebuild
If you want a complete tune up kit (coils, points, plugs wires, water pump, impeller, carb kit) you can get all of that here at iBoats.
Here's another place that will give it all to you at once, but it'll cost $213
http://www.maxrules.com/fixomctunekits.html
If you mean "complete rebuild" as in pistons, rings, bearings, etc, then you'll have to piece that together yourself.