I don't know if it would fit but how about 54mm/ 1:35 scaled miniatures heads? They might work and there are some nice 54mm minis out there. Also
these might be of interest as it is only heads. (found in 5 sec thanks to the mighty google

) And 1:35 scale should roughly be a size of 1,5
cm (0,6 inch or so ...) for heads. That might fit but could also look a little bit to large ... i don 't know. It might look ok as Demon prince models are not known to have realistic anatomy.