As of recently, it seems Blizz has snuffed out every method of obtaining any of these beauties now.
Significant/Popular Pets No Longer Obtainable as of 4/12/12
Armored Battleboar: Completely covered in flames.
The Lone Hunter: Had a knife through his head.
Oil Stained Fledgling: Pitch Black with black fog emitting from it.
Consumed Thistle Bear: Retained it's Pinkish/Purple glow.
Oil Stained Wolf: Pitch Black with black fog emitting from it.
Angered Arakkao Protector: Blue Mist Aura
Kung Din: Chain around neck
Coldbite Matriarch: Sha effect
Corrupted Crane: Sha effect
Ik'Thik Terrorclaw: Sha effect
Amberscale Basilisk: Sha effect
Furious Goat: Sha effect
The list above covers only the pets that kept their buffs after death, since they were the more popular ones. All temporary appearance buff pets (sparklestrider, ghost wolf, etc.) are no longer obtainable through any means.
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NO LONGER WORKS
Ok. So I once again experimented today... and I have sort of good news...
So those Angered Arakkao Protectors with the blue mist? Still tameable with the mist. Having someone kill it for you to make it despawn is a no go though. Blizz seems to have fixed that method for good. Now you have to let the game despawn it on it's own. Timing is precise. It actually didn't take me that long after I figured out this was the only way. Then this theory hit me. Any pet that has a forceable despawn timer can still be manipulated and tamed in a way to keep their buff. This is because people aren't killing them.... WoW is. Blizz nerfed it so PLAYERS can't despawn a pet to keep a buff, but they never nerfed it so the game can't. This theory may mean that there is a slight chance the oil stained wolf is still obtainable...but only through the means of the quest that forceably despawns it.....and of course precise timing with the tame. I personally have had no success with the wolf, but if you would like to attempt/test it more, please do. And please post your results. Feedback is much appreciated.
The bad news is that as far as I know, these two pets are the only tameable pets with a buff ingame that actually have a despawn timer. With the inability for players to kill/despawn pets anymore using themselves or others, it still looks like the flaming boar, lone hunter, consumed thistle bear, and oil stained hawk are unobtainable for good now. The Oil-stained wolf is still unconfirmed, but there is a super small chance it could still work with pinpoint timing, and only using the quest to cause the game to forceably despawn it. But since it hasn't been confirmed since the patch, it will be remain on the retired list until proven otherwise.

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Hello. For those who don't know me, I'm a dedicated fan and longtime veteran of the appearance buff pets, and taming methods. I obtained my first round of glitch pets when Cataclysm first came out, and have been filling my stables with nothing but them since. Lately there has been talk that the latest hotfix (4.3.3) got rid of every method to obtain these interesting pets, and I have been dedicated to figuring out the facts about it.
Ok. I have experimented/tested literally ALL day today with this. I have used EVERY tame method known to mankind in order to attempt to snag the buff pets once again.
Here are my results and conclusions:
2 Person Kill Method: I start taming a buff pet. The millisecond my tame is done, the other person with me insta-kills it, while I spam the nonchanneling revive pet macro. If the pet simply disappeared but did not have to be revived, it would retain it's temp/perma buff. *This was the newest way to get sparklys such as the deviate plainstrider/ghostpaw runner* Result? Fail. I tried this particular method on every known buff pet at least 100 times each since it was the last known method to work. No success.
1 Person Kill Method: Serpent sting/immolation trap a buff pet, and start tame. Pet dies exactly when tame ends. Result? Fail.
I also tried the Petabandon() Macro method just for kicks. Result? Fail.
Quest items/timers used to despawn buff pet: This method includes timing angered arrakao protectors to despawn when tame ends, and oil wolf when quest item despawns it. !!!!THIS METHOD WORKED!!!! With precise timing and patience. But so far I have only been able to nab the mist covered arrakao protector with this.
I even tamed one of the same npc's before attempting to tame another using the methods above, just in case it had any affect like in the past. No good.
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OH and if anyone would like to know the reason for Blizz finally putting their foot down on this method of taming... the answer lies in the Vekniss Soldier of AQ 40...
A few weeks after rediscovering damage dealing buff pets could once again be obtained, a few guilds were clever (or stupid) enough to try something. Vekniss Soldiers emit a Frenzy Aura which increaseS haste and attack power by 20% to all friendly members in the area. When tamed with the exploit, Vekniss Soldiers would give the Frenzy Aura to every person in your raid, causing an ENORMOUS dps boost to the group. If this sounds bad enough, it turned out the buff actually stacked. What this means is that guilds could go and do heroic deathwing, with 5 BM hunters in their group who each had the exploit version of this pet. The buffs all stacked, which would create a MONSTROUS/INSANE 100% haste and attack power increase for EVERYONE in the raid. This started showing up alot in World Logs, and people were obviously getting upset about it. Blizz noticed it, and in seeing past methods of trying to fix this exploit failed, they reprogrammed how tame beast works, ultimately fixing the problem and our pets.
They let us keep our fun taming method as long as possible, but in the end, this bug is what pushed them over the edge.
SORRY FOR THE EXTREMELY LONG POST!
Thanks!