If I was 120 miles from the closest sewing shop I would either cannibalize or make a button. You did miss the other option - hit the button jar. I've been saving buttons for years - buy an extra when I'm sewing things, pick them up off the ground, and then there's the extra buttons that come with ready-to-wear. So I could probably find something in my button jar that would fit. I'd also reinforce the waist band in the area of the button so the new one wouldn't pull out.