The credential costs 1€ and can be obtained in bigger albergues, churches and in the pilgrim’s offices.

Practically:
Saint-Jean-Pied-de-Port: Amies du Chemin de Saint Jacques at 39 rue de la Citadelle (Pilgrim’s office, Accueil Pélerins)
Roncesvalles: Collegiate Church of Orreaga/Roncesvalles (open 10.00 am-13.30pm, 16.00pm-19.00pm)
Pamplona: Albergue Jesús y Maria, Calle de Compañia 4 (Close to the Cathedral of Pamplona)