In 2015 I picked up my copy of Brierley's guide in a shop along the same steep street in SJPdP that the pilgrims' office is on. I can't remember clearly but I think there were other guides there and there were other shops on the same street anyway.
Oops.... I thought it was a Pilgrim Credential that you were wanting. Now I see it is a guidebook. Rick is correct; there is an outdoor shop on the same street as the Pilgrims Office which should have what you are looking for.
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