Try this website, which lists 12 stages.
El Camiño do Mar es una ruta alternativa al Camino del Norte para seguir recorriendo la costa cantábrica y atlántica.
And then what I would do is to take each one of the stages listed and plug the town names into a wikiloc GPS trail search. If you don’t know wikiloc, it’s the site with the most GPS tracks in Spain, by a huge margin. I see that for the first stage, Ribadeo to San Cosme, for instance, there are many recorded tracks.
Find the best outdoor trails for mountain hiking treks, bike tour itineraries, MTB rides, and up to 80 activities. Discover the most beautiful places in the world, download GPS tracks and follow the top routes on a map. Record your own trail from the app, upload it and share it with the community.
If you are not a wikiloc user, these are tracks recorded by people who have walked the routes (usually, but not aways). Some have a lot of textual explanation, some add a lot of pictures, it just depends. Even if you don’t speak Spanish, you can use the tracks to see distances and elevation profiles, which is very helpful.
Our own
@Magwood also walked this route.
And since you’ve already found the subforum for Ruta del Mar, it should be obvious that you will get a lot of info scrolling through the posts that are there, about 40 of them.
Buen camino!