I'm following up on my last post now that I have been to Madrid and back. If you do bring your laptop computer and a portable printer, stock up on ink, software and similar items before you head over.
I had no trouble finding shops that sold the exact model of Canon portable printer I have, but none of them had ink for it. Likewise, a lot of stores have the same model of Apple laptop I own, but none carried Apple-compatible software. As a technogeek friend of mine over there explained, "Spain is different," and the distribution system for IT accessories is still forming.
Since I couldn't print without ink, I went hunting for the nearest local equivalent to Kinko's, which I found just outside the San Bernardo metro stop. It's called WorkCenter (I assume this is a British chain), and is open 24 hours a day.