DuraVent 3BVL90 Aluminum 3" Inner Diameter - Type B Round Gas Vent Pipe - Double Wall - 90" Degree Elbow - VentingPipe.com
DuraVent W2-9006 90 Degree Double Wall Elbow for 6 Inch Inner Diameter Vent Pipe from The FasNSeal Series: Ducting Components: Amazon.com: Tools & Home Improvement
Double Wall Fixed Elbows | Black Stove Pipe Elbows
SELKIRK 6" to 8" 90 Degree Elbow (Double Wall Stove Pipe) – US Fireplace Store