As said above, lots of places provide stamps. I tend to get them whenever I stop for a coffee/Aquarius/vino etc. Your Credencial can then be 'topped up' with stamps from places of more significance if you choose, without any of the 'I need...
On the Camino Frances, every place of business, lodging, recreation, worship and more, will have a stamp. You will catch on, very fast. On other routes, it varies, but the popular routes will have plentiful opportunities.
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