COnsistently over 100 can start as early as late april some years. The best cactus are definately at the Saguaro National Monument east and west of Tucson. Not as many jack asses with shot guns blowing holes in them. The Saguaros up the slope of the catalinas on the left side of SR 77 glow in the evening light. SOme days I really miss living in Tucson.
Tom's links are a great source.