Yeah i buy internal kits. It has the transmission, tube, pen cartridge, and some other pieces. I usually pour my own acrilic blanks, and cut my own wood blanks.
Mostly i just turn down wood or acrylics into the exterior handle piece of the pen. Its pretty cathartic because you end up with a product that reflects your effort and each one will be completely unique.
oh! I can't tell you enough how cool I think this is. I have always loved pens though and have a hard time not spending too much when I go to art stores cause I want to buy all the pens/markers.