Nevermind, I have finally found where the line is. It's in monster.cpp file. Just searched for word 'item' there.
I am not sure how could I have missed it in the first place.
I am trying to change the items which are dropped by the monsters (e.g. when hgrunt dies, make it drop ammo or nothing at all instead of weapon).
However, I cannot find a string in SDK which would determine the dropped item.
How could I change it?