Ok, I’m going to spill my secret for realistic, semi-shiney silver paint. On my pack, I just began weathering and didn’t want just any silver paint, just like you. I went to a hobby store and bought a silver leaf paint pen. The quality is awesome, and the end result is a very metal finish.
Okay, I didn’t have any of my machined knobs handy for this pic but I will dig them up for another shot. These are both resin knobs painted with the aluminum plate paint pictured in Kind2311’s post. I didn’t do any prep work on the knobs so they will look a little rough around the edges.. I gave the large knob a quick buff for the pic and left the small one alone. Few coats of paint and buffing in between can really make these things shine.