There are two add-ons that I know of for sorting through the AH pets.
One is called PetMarket and it's the one I've ended up using most. It adds a tab to your AH interface and a Scan button to the top of it. Once you press that, it goes through the pet section and returns a list of the pets available that you don't have. You select one you're interested in seeing all listings for and click the Show button on the bottom right, then go to the main tab and it'll have all the listings for that particular pet, if there was more than one, of course.
Sometimes, it just doesn't work and shows every pet in the AH. I don't know what makes it misbehave. Usually logging in and out fixes it. But it's too handy to quibble over a few quirks, though.
The other add-on is also useful and was the first I found, but it *sometimes* made my pet battle interface disappear during fights. That wasn't too big a problem as I knew my keybindings and finished the fights anyway, but still annoying. It's Pokemon Trainer, I think was the name. There was an optional feature to set colors to the known and unknown pets--say green for known, purple for unknown. Then as you scroll through the section, you can more quickly spot the ones you need to obtain. It doesn't narrow the list down for you, but makes the ones you want more apparent.
Both have their uses. With PetMarket, you start to not look at the big list and sometimes I wonder what fabulous deals I miss out on because I don't even look at what I already own. With Pokemon Trainer, there's a rather distracting interface added to your battles (but it might appeal to some) and that vanishing skills glitch that can occur. PetMarket can mysteriously refuse to help at all now and then, but it's what I've kept. Even when it shows you allll the pets, it's still a nice condensed version because it only shows one listing of each pet, the cheapest, I believe, but don't quote me on that. I always select a listing I'm interested in and use Show to see all the choices so that bids and buyouts are displayed.
I got both of those from Curse. PetMarket works post 6.1. Pokemon Trainer was outdated before 6.1 and was still functional(ish) so it may work as well now as ever.
Hope this helps!
Add-on for AH
