On Calle Victoria there are a half-dozen or so "reventas" or scalpers. Scalping is an honorable profession in Spain! They have tickets for just about everything, including futbol, charge 20% or so and are in permanent intallations so you you don't have to worry about getting ripped off. They will have all the posters of upcoming events.
If you go to Las Ventas, make sure you know what you are in for. During San Isidro there are a variety of corridas including rejoneadors (toreros on horseback), Goyescas (wearing antique costumes), mano a manos (2 matadors competing), novilladas (beginners) etc. They even have comic toreros!