Guys, I'm really sorry but it seems I used wrong wording in my original post which indeed made my request impossible to fulfill. I used term 'rare' pets, but meant 'capturable wild pets' as opposed to the regular ones available so far in game from vendors, quests, events, craftable or from Blizzard store etc.
Thanks for responses though, it was a good read! Especially the quote from forums
It made me dig for some more addons and found one that indicates the pet's rareness before trapping (
Pet Battle Quality Glow - so far it worked perfectly).
Anyway, what I'm looking forward is a map, that would merely indicate pets' spawn points within the zone, just like the wowhead map. So that I don't need to constantly alt tab to browser. It does'nt need to have fancy options, be highly interactive, just symbols for pets so I can know where to look for that particular pet throughout the zone.
Hopefully someone will develop such a map addon soon