Thanks for all the responses thus far. I actually found a UK based agent who sells Dart 18 square tops for the Dutch sailmaker, Landenberger. Prices are competitive, the sail plan looks strong, and they can build in a variety of materials. Check it out - http://www.cat-bitz.co.uk/

They also have dart rudder rebuild kits (thank god).

The only thing I don't know is what (if anything) this will do to my portsmith rating.