Because there are so few black flowers that are available as CUT STEMS for event use and personal arrangements, an alternate option is to utilize the CENTERS of flowers as BLACK ACCENTS.
Here are several flowers having black centers that are also usually readily available as CUT STEMS:
Anemone (White, Blue, Red, Pink, or Purple petals)
Available: December-March
Black Eyed Susan
Available: June-September
Gerbera Daisy (Petals of varying colors)
Available: Year Round
Sunflower
Available: Year Round
Oriental Poppy
Available: January-March