Carlon Multi-Gang PVC Electrical Box Extender (2-Pack) B1MGEXT-2 - The Home Depot
Multi-Gang Switch Box, 2-Gang, Two and One-Half Deep
1 Pc, 2-1/8 In. Deep, Three Gang Multi Device Switch Box, .0625 Galvanized Steel, (4) 1/2 In. & (6) 1/2-3/4 In. Side Knockouts; (2) 1/2 & (2) 3/4 In. Bottom Knockouts - Amazon.com
1 Pc, Zinc Plated Steel Three Gang Multi-Gang Box Cover, Cover, 1/2 In. Raised to Mount Multiple Devices - Amazon.com