Bike Seatpost Adapter Shim Bicycle Seat Post Tube Adapter 22.2mm/25.4mm/27.2 mm/31.6mm to 25.4mm/27.2mm/28.6mm/30.4mm/30.8mm/31.6mm/33.9mm/34.9mm Seatpost Reducing Sleeve Shim for Mountain Bikes Seatpost shim-22.2 to 25.4 mm
Colorful Aluminum Bike Seatpost, Folding MTB Seatpost, Road Seat Post, Bicycle Component Accessory, 600mm, 31.8mm, 33.9mm - AliExpress
Amazon.com : Bicycle Seatpost, 33.9mm Aluminum Alloy Adjustable Folding Bike Seat Post Tube for Cycling Road Mountain Bike (Black) : Sports & Outdoors