Hope Head Doctor Into Steerer Tube Extender - YouTube
Amazon.com : CYSKY Bike Stem Riser 28.6mm Bicycle Fork Stem Extender Aluminium Alloy Adjustable Handlebar Riser Adapter for Mountain Bike, Road Bike, MTB, BMX, Fixie (1-1/8" Black) : Sports & Outdoors
Amazon.com : LERWAY Bike Stem Riser Extender MTB Handlebar Stem Adapter with Hex Key for 1-1/8" 28.6mm Fork Aluminum Black : Bike Stems And Parts : Sports & Outdoors
steerer - Are stem height extenders safe to use? - Bicycles Stack Exchange