Most likely, it's the room dto the right of the starting area. As soon as you enter the door, look down below. The other four are in the last four rooms leading up to and including the room with the door you are decrypting. I encourage you to try to finish it up. There's a good number of jokes left that you haven't seen yet.
I plan to put in an extra item that EMPs all of the monsters (disables all encounters for the rest of the game and levels you up to 10) or something like that.
Thanks for checking my game out. I hope you're able to finish it.