These drop off of the "Large Brown Rats". I haven't had an issue finding the whiskers once I found the right rat to kill. There are a few close to to AVP zone line.
In my honest opinion think they reverted the drops/chance on the windblade, 9 days ago I killed him 3 times and got the blade 3 times in a row. Today killed him 3 times got it once.
This mob has THREE spawn locations. I will reference them as #1, #2, and #3 below. The thing most people don't realize about this mob is that there is more than one spawn because TWO of them (#2 and #3) aggro the nearby Ogre Infiltrator mobs and die about 25% of the time when they path by the Zarnak Stones. Day or Night makes no difference and there are no placeholders for this mob.
Wandering Wildspell #1: Spawns at 2340, 1978 <--- Paths to then turns around at ---> 2461, 1806
Wandering Wildspell #2: Spawns at 2456, 1934 <--- Paths to then turns around at ---> 2647, 1714
Wandering Wildspell #3: Spawns at 2504, 1776 <--- Paths to then turns around at ---> 2576, 1504
Out of roughly 50 kills of these I have seen the Chaotic Imbuement spell drop three times. (Roughly 5% drop rate)
~ Stormchance <Fallen Crusaders>
Enchanter, Dark Moon Server
The Schematic for this item claims it requires a "SIMPLE BOW GRIP". No such item exists by that name in the game. What it's ACTUALLY wanting, is a Thick Leather Bow Grip, which is sold by the Fletcher but ONLY CRAFTABLE by an Outfitter (derp!)
This schematic is not sold Anywhere. It's a REQUIRED component of the "SIMPLE CEDAR LONGBOW". Fletcher sells the T4 bow grip schematic, but NOT this one. Apparently based on the "Lifebound" tag above, it's a rare drop from somewhere and it's not tradeable!
I killed the placeholder for about an hour on two different shards before he spawned. My biggest takeaway was that it takes 15 minutes up to 17 minutes for it to spawn. Good luck!