A few years ago, Dani Carbonell gave a training on gralla and, at the session devoted to reeds, one of the attendants -I do not remember who it was- wrote some notes which we all considered very good and eventually ended in photocopy form. Click for a copy of them, Notes on the finishing of reeds (if the author makes himself known and claims the copyright, then I will have to take it off).
Drawings by Roser Olivé of the Reeds at different historical profiles.
At the Web of Grallers de l'Aleixar, you will find a writting about The reeds for gralla, with many advices on how to give a good finishing to the reeds.
In this Web by the Tirallongues de Manresa there is a gralla page, on which you will find information on reeds, staples, and their manufacturers.
The description of the instrument, as it stands on Wikipedia.
The various types of gralla, at grallers.cat.
Short Description of the Evolution of gralla.
Luthier Francesc Sans's webpage, where you can see his differant types of gralla, including models with diferent number of keys.
List of gralla and reed suppliers, also other instruments and accesories.
Quatre notes, miscellaneous information about the gralla and traditional music.
Els grallers, a blog written by José María González with very interesting articles, scores and links.