If you really want an odour of decay, rot and genereral foulness, I can let you have a pair of my old socks... reasonably priced... no carriage charge, I just point them in the right direction and they'll walk there themselves...
However, I can certainly confirm that the BlackHart products are excellent, try mixing a little of the two aromas together, or have a few drops on a lightbulb so when it's turned on the scents are vapourised into the room.. very unsettling! An oil burner can be another most effective method of adding the scents to a room, try adding a minute drop of lavender essence and you have an instant foul old lady smell (apologies to all foul old ladies reading this).