I have purchased premade gumpaste white flowers, I need to paint them black (could not order black ones) what is the best way to do this. I do not have an air brush.

You can use a paintbrush and paint them with black airbrush color, or dip them in black food coloring if they're sturdy enough.

just to add a little detail -- when i dipped flowers -- into a glass jar just bigger than the flower i added enough air brush color and everclear to submerge it (or vodka -- alcohol facilitates drying) -- i had my blow dryer ready to start most of the drying -- when dry  i would brush with pearl and steam -- in this case i would brush with black petal dust and steam --

if you use a jar with a nice tight lid you can re-use the mixture