Just found a Vietnam era A1 buttstock that I want to put on my AR (the A2 stock I currently have is too long - and yes, I also bought the shorter upper screw to go with it). It has the expected age wear and scratches you might expect from a 40+ year old item. I want to sand out the worst of the scratches and refinish it (in basic BLACK). Is there any particular rattle-can paint, preferably something I can pick up at Ace Hardware, Walmart, Kmart, or even the local car parts store, that will work well?

Use 1500 or so grit and wet sand. See what you think of it before committing to paint. If you do choose to paint use Krylon Fusion 12 oz Spray Paint (But not gloss )