Mobs can be found at oposite side of Emerald Sanctuary (easier to farm and kill, shorter to run from spirit healer). There are lots of mobs on the top of the map at Felpaw Vilage, but there are more chances to be ganked by alies, and the way is much longer from spirit healer.
P.s. sorry for english mistakes :}

As of 3.0.2 this gives 300 rep per turnin at level 70.

TURN-INS GIVE 300 REPUTATION NOW. YOU ONLY NEED 350 FEATHERS OR BEADS to get through revered.
Ignore any guides below saying that you need more. Those guides are old.
Mobs only give reputation through Honored, so save your feathers/beads until you get 350 total, at which point you can start turning in the excess.

To be able to collect feathers for the handin quest, you have to complete https://vanillawowdb.com/?quest=8461 Deadwood of the North. After this quest is complete, you can collect feathers for a handin quest for reputation.

With the changes in 3.0.8, as the poster above said it takes 350 feathers to get exalted from revered.

Now we talk strategy.

If you make 20 rep (22 for humans) per kill, excluding the Chieftain, and the drop rate on feathers is 40% (using the northern farming area in felwood, as it's better), then it'll take 875 kills (800 for human) to gather enough for revered -> exalted. You do not get rep from kills after honored. This 875 kills will get you approximately 17,500 rep before turn-ins (+100 more for Humans' 800 kills). My advice: Do not turn in any feathers until you are revered. By the time you've gathered enough feathers for the revered -> exalted turn-in, you will already be revered without turning in anything.

Going over the numbers again:

Feathers needed to go from Revered -> Exalted:
Non-Human: 350
Human: 320 (rounded up)

Kills needed to gather needed feathers for Revered -> Exalted:
Non-Human: 875
Human: 800

Rep gained from kills while gathering feathers to go from Revered -> Exalted:
Non-Human: 17,500
Human: 17,600