To polish locks and hardware I use these:
small 3 corner file
flat Swiss fine file
needle files
diamond files
diamond knife sharpeners
emery boards
I don't use all these on every part, just what seems to be biting best at a given grit level, if that makes sense. The diamonds work on the hardened stuff, though it can take a while. I do reshaping with a small stone wheel in a Dremel tool. The diamond knife sharpeners will keep flat areas flat and corners sharp.
Emery boards will go all the way to near mirror finish if you want.
I do all this by hand, so yes, it takes a while. What else am I doing in front of the TV?
The emery boards come from the local grocery store cosmetic department. Skip the coarsest ones and get a few each of the finest. Use wet or dry. clean with soap, water and a toothbrush.
This works for me, hope it helps others.
John