This is a class I once sailed in and at the time there were two builders of this one design and you could get your sails from any sail maker as long as the sails measured in and the royalty was paid.

Interesting approach:

* The Thistle Class Association is sponsoring a raffle for hull #4000. A
maximum of 500 tickets will be sold for $100 each. The winner will
receive a ready to race Thistle, with trailer and all rigging (without
sails or covers). For rules and an entry form, visit the Thistle Class
web site at http://www.thistleclass.com/articles/raffle.pdf