Check the Home Built Bazar attached to this website.  In early May someone, I believe in Vermont, was selling a tandem.

Good luch

Paul

This one may still be for sale:

http://www.flickr.com/photos/algonquinpaddler/

If you live anywhere close to wash state, you  should look at our boat.

 see:

http://www.angelfire.com/nv/wongnumber/doublekayak/doublekayak.html 

If you look right above the list of posts, you will see:  "for the home built bazar, click here"