Rachel, nearly every shop, cafe-bar, hotel, hostel, inn, library, police station, tourist office, church, municipal office, albergue etc etc have stamps.
There are a few well known ones - like the Felisa stamp which is offered by Maria as you walk into Logrono. Felisa died in Oct 2002 but her daughter took over the table outside their ramshackle home and still offers "Higos, Agua y amor (Figs, water and love).
Then there is Marcelino Lobato's stamp. When he isn't out walking a pilgrimage route in his long medieval robe covered in badges and shells, upturned hat and staff - he sits in a 3-sided hut in the woods outside Logrono offering fruit, nuts, biscuits and, sometimes, walking sticks, and a stamp.