Redridge Rat

After three days of searching, I finally found mine: crawling around the feet of what i'm pretty sure is a stationary npc, standing between the bones of some large animal. The npc is Rabid Shadowhide Gnoll by Keeshan's Post. I hope this helps!

This is quite possibly one of the hardest rares I've hunted so far. The tips about them being mostly in the gnoll camps is totally correct and that is where I eventually found a rare one (the camp near the FP). Got a very few as secondaries but they were all poor.

entered battle with mountain cottontail...had rare RR as second yay!...it suddenly changed to gray...ugh what gives!!

Found a poor quality one by itself near all of the sleeping worgen at Alther's Mill

Found mine in the gnoll camps in Three Corners (south-western corner of Redridge) after a good deal of searching.

Got my rare by battling a Mountain Cottontail and the Redridge showed up as a secondary. Took many battles with no luck of a rare, but be patient! :)

First one I battled had 2 rats in one fight one of them being a rare. Which I killed :( havent found another rare since.

Keeshan's Post was successful for me.  There appears to be about 3 rats as primary spawns.  I got my rare at 67.32 at 12.15 pm (Oceanic) after about 20 minutes.  I also battled all other types as the rat can also be a second.

Your best chance of finding one in Redridge Mountains is around Keeshan's Post (upper right corner of the map) where the Gnoll camps are. There are also several Mountain Cottontails and Roaches who tend to have them as back-up. The respawn is also quite fast. I found my rare there, a lvl 4 with 257 health. I didn't expect it to be rare since I battled several lvl 5 rats with 306 health and they turned out uncommon. Good luck!

Found one as a second to a battle with a lvl 5 Roach.  Poor quality, but I'll take it for now seeing as it was the only one I could find after sweeping the zone 3 times.

Caught 3 rare Redridge Rats in Render's Valley.

1 pure black and 2 colorchanger (black & brown: both were combat joining pets)

Couldn't find one anywhere, so I started fighting the Mountain Cottontails hoping for a rare, but after a few battles ended up catching this rat cause he was backup for a bunny :)

Found one by the huts just north of Stonewatch Tower. 

I found him at Alther's Mill. There were 3 of them just sitting there in the group of elite dogs. I couldn't click on him at first and made the mistake of using swipe and killed all 3. They respawned about 10 minutes later and I was able to capture him.

This rat is very challanging to find.   They are super rare in this zone, and none of the ones that spawn in the cave seem to give you the icon for pet batteling.