I found a way to trigger the randomness of regular bonecharms. If you have some free time, maybe you can test that out to see if you get any of the bonecharm we haven't confirmed yet.
In A Crack in the Slab, render Stilton unconscious then pass the upper doors to get back inside the manor. Now, saving Stilton will make his new office appear on the map in the present, with a bonecharm on his desk. Each time you reload the auto-save made after entering the manor, the bonecharm will be a different one.
Another place where it might work is when entering the Dust District after completing A Crack in the Slab and saving Stilton. 2 regular bonecharms and 1 black bonecharm appear in that area and there's no guard around.