Those Nitto Pearls are mighty nice stems, but they don't come cheap!
OTOH, if you found your ideal stem except for the color, I'd try to find a powder-coater who could add a small thing (like a stem) to a batch of black he's shooting...you'd also want to mask off the clamp areas, but PCers can do this.
PC will be much more durable and aluminum alloy is notoriously hard to paint well with rattlecan paint.