Peaceable Projects Inc. is a U.S.-based non-profit group that brings the vast resources of the wide world together with the ongoing needs of the people who live, work, and travel on the Camino de Santiago pilgrim trail network in Spain.
An interesting one to look for in Paris is Aux Vieux Campeur. They have stores throughout the Latin Quarter. Otherwise any of the major department stores (BHV, Bon Marche, Fnac, Galeries Lafayette, Printemps, Samaritaine) will have an outdoor adventure section and that might be easier if you just need a few items.
And you can buy compeed at the pharmacie in Paris as well.