An age-old adage says that Necessity is the mother of Invention. Although having a tattoo gun does not essentially qualify as a necessity, yet the inmates are pretty resourceful when it comes to styling a tattoo gun out of nothing.
You give a prisoner a Walkman, some paperclips, a few rubber bands, and a Pen; and you will be rewarded with a fully functional tattoo gun. See the video below as the tattoo gun is assembled:
Bu first, we need to find that Walkman!