A quick and mostly working skeleton rig that I added to ndrs's Alduin model. You should be able to pose and scale most parts however you need. If not, you can always extrude new bones.
This was all done with Blender, which is Free and Open Source. Use the .blend file within to pose the dragon. Once posed, export it as either a .OBJ or .STL to prepare for your printer!
This is the other Skyrim dragon I rigged, in case you want something less spiky