After looking into the current state of 3D-printed gun-making, CNET's Rich Brown asked the various 3D-printing services about their policies toward printing firearms and firearm components.
[Philip Lelyveld summary -
i.materialise - no
Ponoko - maybe
Sculpteo - no
shapeways - no
3D Systems - no response
Thingiverse (MakerBot) - no, but their software library contains gun part designs ]