you could camp the 2 that spawn at the zone.
and then wait 20 minutes for a respawn.
sure, eventually you will get the drops.
i think i might pull all my hair out first, tho.
or you could be intelligent and move in and kill the 10-15 more that are up in the zone at any given point. they share spawn points with cragbeasts, so kill these if they are up.
you will have to break past an unsnareable see invis ukun/kyv duo at the entrance, of course.
there will be more hynids just past here, then make the first left. the hynids/cragbeasts are near the wall of the zone, all around the central area. it is very easy to kill them without aggroing anything else. (but take heed at the building near the oddly potted tree in the corner)
i got my 3 pristine hynid manes within 5 hours.