I encountered the same issue but was able to fix it: I placed a random Sim on a lot, opened the cheat bar with Strg + Shift + C and used the following cheats:
testingcheats true (as always)
bb.moveobjects (to place the sword on the floor)
bb.showhiddenobjects
bb.showliveeditobjects
I entered the Build Buy Mode and typed Simcalibur into the search bar and purchased the sword.
My Sim wasn't able to pick it up as it didn't belong to her, but put it in her inventory when i clicked "mount (sword)". I was on an empty lot without any walls.
With the sword in the inventory I traveled to the rock and chose the option to put the sword back by clicking on the rock.