My experience was from a few years ago, when I walked the Levante with two French guys who could not conceive of life without a 10 am stop for a coffee. We started in Valencia, and they used it only for making coffee. By about a week out of Toledo they were using my electric coil to heat water in the morning and saving the jet boil for the stops along the way. They found (and things may have changed) that the particular kind of gas canister the jet boil uses was not available widely. Only in Decathlon, and as Felipe and jozero have pointed out, those stores tend to be in big cities. And most of them are not well placed for the pilgrim on foot, usually out in big industrial zones, though there are a few in-city locations now (Zaragoza and Lisbon both have them in-town, so I'm sure there are others).
But if you are going to be continuing on the Vdlp after the Mozarabe, you will hit big cities fairly frequently so you should be ok. Buen camino, Laurie