Where is the blade of the equalizer??? I've got the hilt and the pommel jewel. I'm currently just out of the Illithid Arena, killed the ogre.

Question No. 2: What is the best and most risk-free way of killing mind flayers???

The blade of the equalizer is on the corpse of an elder orb beholder, in the beholder lair. It's just south of the entrance to the illithid lair, and the elder orb with the equalizer blade is right at the dungeon's entrance. Careful with those things, they can imprison you.
I still haven't found an 'easy' way to kill illithid. I thought using stoneskin and mirror image with my fighter and then chopping them up systematically would work, but even if they don't actually do damage to you with their attack, they still drain intelligence. I have absolutely no idea. You could use potions of genius and mind focusing to give your characters more time to fight them before they finish munching on your brains, but that's all I can think of, aside from summoning a Mordie's Sword to take them all on. Just make sure you cast chaotic commands on the sword.