There are a few other places with scarecrows aside from what I've seen posted here. If you head over to the Estate of Unrest there are a few, but personally I would more than likely just stick with Dragonscale Hills. At the farm camp there probably spawns about 6 or so Scarecrow mobs per cycle. Respawn timer is about 20 minutes IIRC. Happy Slaying :)
Oh and I have to agree with Lovguild, reposting the exact same information that the site developers input for a quest or item is pretty lame. Amio has done this on almost all of the slayer achievement quest listings, very lame.