Your best bet would probably be to get your hands on a set of oversized buttons. Some of the more independent builders use buttons that they make themselves out of the little metal caps on the bottom of furniture feet. Some are bigger than others. Quite frankly, I have a difficult time playing an accordion that is fitted with these because my hands are big and the buttons scraped the sides of my other fingers. Maybe Jude might know where to find a set. You could even go down to Home Depot, get some caps yourself and glue them over the existing buttons.