User blog comment:Mr Stickman/Q&A Returns/@comment-768817-20130416030621/@comment-4470623-20130416165340

It's a rare item. It shows up randomly like every other item in Skyrim. Though it can only be found in Dwemer ruins. It's entirely possible that it may not show up the first time you go through them and it may require several run throughs of each of the ruins. Make certain to search for all the hidden chests as well as it is more likely to show up in those.