Orbit 5SDB-MKO-EXT Electric Box Extension Ring, 2 1/8" Deep w/MKO Knockouts - 5" Square - - Amazon.com
1/2" Octagon Box Ring Extension - - Amazon.com
1/2" ReceptXtenders (one), Single Gang Receptacle Outlet Box Extender. UL Listed, Mud Ring by WGDepot - - Amazon.com
Hubbell Raco 8201 4" Square Extension Ring - - Amazon.com
2 Pcs, 4 in. Round Pan Box Extension Ring, 1/2 in. Deep, Zinc Plated Steel Used to Mount Ceiling & Wall Lighting Fixtures to Provide Additional Wire Capacity - - Amazon.com