D&B,
The bullfights are on sundays, at least in Las Ventas, the biggest and more reputated in Madrid.
I include this link for you to read if you know Spanish:
Plaza de Toros de Las Ventas I think they have never been suspended because of the disease, it was only forbidden to sell the bodies of the bulls for food proposes. Even that could be off by now.
You can easily arrive by metro or bus. There is a map in the web I posted above. It is in the eastern part of Madrid's downtown area.
You can buy them at the Plaza de Toros os some authorized agencies (I don't know any), these can charge you up to a 20% extra.
Of couse, you should buy in advance or very early or you will have to buy them to ilegal resellers around the Plaza, usually 2 to 4 times its usual price.
Prices:
Prices in pesetas The closer to the ring, the more expensive. Also, if you are in a shadow area (much less hot), it is more expensive. 'Sol' means 'sun', 's y s' means 'sun and shadow' (depending of the hour), 'somb' is short for 'sombra' - 'shadow'.
Hope this helps