You might get lucky on the shoes, but don't count on it. I even went into Foot Locker in Madrid, and they just looked at my 13 1/2 Ws and laughed. They told me that they didn't have anything that exceeded the equivalent of an American size 10W at that time. Of course that was in 1998, so things could have changed since then.
You might want to do a little "on-line" checking on this issue. It's very possible that you will be able to find stores in the major cities that cater to the larger foot.
Anyway.... times.... they are a-changing. Who knows for sure? Maybe one of our local Madrid area residents can check the sizes when they wander through stores, and post something that can be helpful.
If not, you could always do like a friend of mine suggested. "Can't find shoes? Buy a couple of surfboards and tie them to your feet."
Wolf