Any sighting of the elusive Big Cat?

Yea..
Found Jaira Mob ID in Mob.wz,
But it didn't tell anything about the spawn.
or maybe i'm just too dumb to read the whole thing. >.<

I'll just leave this here:

The WZ files do not show Jaira spawning. If it spawns, it's from a server sided script.

There are five ways you can tell that the Jaguar you are seeing is indeed Jaira:
1) Glowing eyes
2) Jaira is very black - more black than the blackest standard jaguar.
3) When you attack it, you do only 5 damage compared to 25.
4) Because of #3, you can knock back a standard Jaguar, but you cannot knock back Jaira.
5) Jaira also has a lot more HP. He has 300 HP, so it will take more than 50 whacks to capture him compared to a normal jaguar's 3.

Also, looking at the files, I only see one map where jaguars spawn.

You will have to be quick to get him. The WZ files state that once Jaira spawns he gets removed from the map after 15 minutes. So if he only spawns once per day per channel, that's not a very big window.