The first piece of the Greater Patron can be found in the Second Floor Weapons Shop.
The second part can be found on the 3rd floor in the room with air riders.
You can get it by jumping from one trolley to another. Yes you can ride them!
The third part can be found on the third floor in a large room with invisible floor.
You can get it if you have a weapon that leaves a mark on the floor or, as in my case, on an obum. 🙂
The last part can be obtained by killing the last boss and destroying his skull.
I think everything is clear here.