M-D Turn Buttons For Screen Frame in the Screen Frame Connectors department at Lowes.com
Wright Products 1-3/4 in. Half-Turn Buttons (8-Pack) V20A - The Home Depot
4-Prong Nylon Plastic 4-Hole Turn Button Washers — Fastener Line
Saint-Gobain ADFORS 8-Pack White Nylon Window Screen Turn Buttons - Replacement Clips for Holding Screens or Glass Panels, Weather Resistant in the Window Screen Clips department at Lowes.com
Prime-Line White Nylon Turn Button (100-pack) PL 14638 - The Home Depot
Prime-Line Black Turn Button Screen Clip (12-Pack) - Connolly's
Door Twist Lock Latch Nylon Turn Button for Boat Door Cabinet - Walmart.com