36"W x 13 1/2"H Triangle Gable Vent (51"W x 19 1/8"H Frame Size) 9/12 Pitch: Functional, PVC Gable Vent w/ 1" x 4" Flat Trim Frame - Walmart.com
Ekena Millwork 48" x 22" Triangle Gable Vent: Unfinished, Functional, Smooth Pine Gable Vent w/ Brick Mould Face Frame GVWTR48X2200SFUPI - The Home Depot
Metal Gable Vents - Vulcan Vents - Fire and Ember Safe Vents
Does a Roof Need a Ridge Vent? - Fine Homebuilding