Duststalker is a level 8 aggressive rare cat that can be found in southern Teldrassil east of Gnarlpine Hold. (I have indicated where he can be found in red on the map below.) He is especially desirable as a hunter pet as he looks exactly like the Spotted Frostsaber mount as you can see in the screenshot above.
Duskstalker can be found with NPCScan. You will need to add it, his NPCScan ID is 14430.
You can also use this macro to help find and tame this guy:
/cast Tame Beast
Although Duskstalker is rare, he is on a pretty short spawn timer. It seems he can spawn anywhere from 30min to about 1.5hours since he was last tamed or killed.