Why can't a master blacksmith, or even a relatively competent one, make his or her own lock picks? i bet you could make a stack of picks out of 1-2 bars of ore, and each higher level of pick would have better force %, and longer duration against the harder boxes.
Make the picks available depending on progress in the Legerdemain skill line so that everyone isn't just running around with voidstone picks, but this would be a nice immersion addition to be able to have better, more expert picks.