Not having done this route myself, I cannot say for certain. That having been said, every entity in Spain has a sello. When I was on the little-travelled Castellano-Aragonese, I had no trouble gettings sellos. Of course, albergues will have them, but so will pensions, hotels, bars, and restaurants, as well as any museums or churches you might drop into along the way. I found ayuntamiento (town hall) staff always happy to stamp away and I was occasionally given a cup of coffee. Police, whether municipal or Guardia Civil, were also pleased to provide sellos and frequently gave me golden advice on how to find the way of the Camino out of towns, which is not always well-marked. A certain forum member is proud of her rabbit abbatoir sello, which she believes is unique.
In short, you'll be fine.