The blackest thing is lens flocking, which you can get from in small sheets for tabletop subjects.

If this is for people, I just use superwhite seamless and black seamless, and to get the superwhite really bright, I just put more light on it, and to keep the black black, be sure to keep the subject far enough away from the lights and to control the light with barn doors, flags, etc. to prevent overspill. Even grey seamless can produce a clean white, if you keep it two or three stops brighter than the subject (by reflective reading, depending on how contrasty the film is).