Make your own rounded plugs
For convenience, cost-savings, and the ability to utilize uncommon wood species, I like to make my own button plugs. I simply chuck a dowel into a drill, place a small square of abrasive on an anti-fatigue floor mat, and sand the dowel end to the shape of an M&M candy, as shown. Don't press down—allow the weight of the drill to do the work. Start with a coarse abrasive and work your way up to 220 grit.
Cut off the button at your bandsaw. You can also make small square buttons so long as your drill chuck is large enough to hold square stock.
—Tony Rush, Springfield, Ore.