Sometimes hotel staff will sort you a ticket if you give them a tip. Last time someone with us got one that way and it was printed off from the Internet. At the turnstiles pretend you are a German or French tourist. Madrid and Barca CL games are just full of tourists. The more expensive the ticket you buy the less hassle you will get. At Barca for one match I bought one off one of those city-centre kiosks and no one asked me for any ID. I believe there are similar ones in Madrid.
Cheers Bobby. Will give this one a go if i cant obtain before flying out. Do you fancy the Costume Musuem or the Archaelogical Musee. Not sure we will all have time for both?