Attempted to book my Madrid Card for my trip end of next week. Web site does not open, other sites are showing card as unavailable. What has happened here? If not available guess I need to book some timed entries very shortly.
I used the Paseo del Arte card (just covers the big three) last year. I simply walked right up and bought it at the Thyssen, which I figured wasn't going to be terribly busy. I was in Madrid in mid-May and may just have been lucky, but I went to all three museums--including twice to the Prado--and never encountered a line worth mentioning. One of my Prado visits was on Museum Day, when entrance was free. I can only assume that MD wasn't well publicized. There were significant knots of people in front of Las Meninas and Bosch's Tree of Life (title might be wrong), but otherwise the museum wasn't crowded anywhere.
The most crowded site for me, still without a bad line, was the Palacio Real. My sense was that it is very popular with Spaniards. For what it's worth, I didn't care for it at all, but palace furnishings usually don't appeal to me. When will I learn to skip them all?
How did you try to access the card purchase? Go to any of the three museum websites and they list the options with further informatiom. You have to line up and pick it up at the museum you 'bought' it from, so you may need to know your sequence of museums visited, or do an extra trip just to pick up.