If it’s a decent quality reflector and strong enough you could use an M8 or M6 bolt with a fibre washer so the bolt and reflector could be held in a drill chuck to make the polishing easier. Use a thick steel washer the same size of reflector on the outside
Don’t press too hard as you wouldn’t want to buckle it.
The reflector is chunky aluminum, the Colrui
Yes hardware store it is and browsing the car department (we have it scheduled today
I fear my drills vibrate too much but it should be doable to mount it on my heavy tool with two stone discs I use to sharpen the axes, shovels and scythe with. Nice solid tool that spins rather fast.
What about something like aluclad that the model aircraft guys use?
Painting it is a waste of time and paint. The amount of time you spend waiting for it to cure to the point where you can begin to spend yet more time polishing it to a not as good as polished aluminum finish would exceed waiting for two successive orders of reflectors. Please don’t confuse metal colored with mirror finish. Or, go ahead and do it, it’s your time to waste.