AprilYSH's Spiral Curls hairstyle is perfect for dreadlocks, and is only $5 at 3-D Arena. Well worth the price. You could probably fit it to male characters with minimum effort. Look here for preview pictures.

whitemexican has some dreadlocks for male characters here at the Marketplace. He had some in Free Stuff but I think they've been removed.

You can find a dreadlock texture and bump map in the Free Stuff over at 3D Commune by GnarkLeFourbe, but it doesn't come with an actual hair object.