I've never heard of a camera user needing to purchase a 3rd party lens mount, but with Sony, apparently, its bad enough to warrant a 3rd party making a replacement.
Generally, lens mounts are considered to be very critical, Canon service manuals devote processes for aligning, measuring and shimming them to be perpendicular to the sensor, and the exact distance to sensor is critical as well. Apparently, even a Chinese made ring will be a improvement to the plastic thing that Sony uses, alignment or not.
http://www.fotodioxpro.com/tough-emount-from-fotodiox-pro-replacement-lens-mount-for-sony-nex-emount-camera.html
Generally, lens mounts are considered to be very critical, Canon service manuals devote processes for aligning, measuring and shimming them to be perpendicular to the sensor, and the exact distance to sensor is critical as well. Apparently, even a Chinese made ring will be a improvement to the plastic thing that Sony uses, alignment or not.
http://www.fotodioxpro.com/tough-emount-from-fotodiox-pro-replacement-lens-mount-for-sony-nex-emount-camera.html