Sea Gull

It's now easy to find a rare leveled-up sea gull right in your garrison, at least as Horde - not sure about Alliance. There's a battle with a level 25 sea gull in your fishing cave. It respawns fairly quickly.

In Tanaris, these appear as Primary spawns only near the water. The map is not accurate - they also frequently spawn on the offshore islands and sandbars in many places not marked on the Tanaris map. They will also appear as secondary spawns anywhere in the zone. I had major trouble finding a rare ... possibly because Tanaris spawns only contain two pets. They share spawn points with trash level 1 critters, so be sure to clear those out as you go.

Very Minor Annoyance Time: It's Seagull, not "Sea Gull". One word, Blizzard.

Found a rare at Lost Rigger Cove in Tanaris (71.3,45.6) sitting on a cage outside the north fence.   It had a rare Gold Beetle as a secondary.

cyclone and lift off

This pet is very hard to find as a rare. It seems to always be a secondary pet. I got this rare while farming the Sumprush Rodent. This pet sprawned at least 4 times as a rare

I've found the best hunting zone for this one is the coastline of Tanaris and just slightly inland. Finding them is pretty easy but getting a rare, not so much. It took me about 2 hours just to find an Uncommon one so be prepared to spend some time on this one!

Caught a rare one and named him Steven, he's actually a pretty good pet though a little overweight ;)

Found this as a secondary to a Darkmoon Glowfly. I had no idea they even existed before then.

Found mine as a level 6 secondary to a Darkmoon Glowfly on Darkmoon Island.

I hunted this for hours killing in and near booty bay, killing crabs and beetles. Then in stormwind. Finally, went to Tanaris and got one within 5 minutes on the shore. I thought I had to be in the EK to get the Eastern Kingdom Safari achievement but I was wrong. You still get credit even tho catching this in Kalamidor. 

You need to go to Tanaris, I got one as another pet that joined battle in Tanaris and didn't know they were "hard to find" and figured thre are seaguls everywhere! Ppppffff well I spent an hour hunting for another... Then I checked location 64,60 (it's pretty much on the shore line, like 3 feet from the water) and there was the seagul with a seagul buddy...Both were lv 13.

This joined as a second pet when i was battling a Stripe-Tailed Scorpid between Gadgetzan and Sandsorrow Watch. Decided to tame the gull instead, seeing the comments on here. Got a rare first time, but pretty sure thats down to luck.

got it on the docks of tanaris -- a rare on my first battle!

Gave up looking around Stormwind and Elwyn Forest for one, and got it as a second critter in a battle in Tanaris. Havent found any others as yet on their own, but at least you know you can get one if you fight other creatures here. Got mine at about 22:35 server time.

Found in Tanaris, at 64,60 after flying nearly the entire coastline and starting to think I would have no luck here. Pretty easy capture with the team I have of lvl 13s. Happy hunting! 

Try checking around the Stormwind docks too!