They're not commonly hunted just for the sake of hunting them because they come in groups and are often casters. They appear in many zones, as noted here:
http://wiki.project1999.com/A_shadowed_man
Specific locations of some of those:
Innothule: underwater, near one of the giant hands, IIRC
Nektulos: in a valley near the EC zone line
WC: in the southwest corner of the zone