So, in order to join the Companions, they say I must find this Kodlak guy. However.... I've been looking everywhere and he's nowhere to be found. By now, I'm thinking it has to be a bug of some kind. I'm playing the pc version, so is there a console command to make Kodlak spawn and finally start the quest to join the Companions???

Go into the companions guild hall in Whiterun, I forget the name. At one end of the structure there will be some stairs going down into the living quarters. You will find him at the end of the hallway chatting with another companion.