E-Simpo® 6pcs E14 to MR16/Gu5.3/G4/Gu4 Adapter EU Candelabra Base E14 to MR16 Spotlight Bulb Base Holder Socket Converter,Ceramic, Make Sure The MR16 Lamp Working Voltage is The Same as E14 Socket - -
E-Simpo E26/E27 to MR16/Gu5.3/GU4/G4 - Standard E26/E27 Edison Screw Base to MR16 GU5.3 Base Adapter Holder Converter (Aging Adapter) - - Amazon.com
E-Simpo 10PCS E26 to Gu5.3/GU4/G4/MR16 Adapter- Standard E26/E27 Edison Screw Base to MR16 GU5.3 G4 Gu4 Base Adapter Holder Converter (PBT Material) - - Amazon.com
10 MR16 GU5.3 MR11 GU4 12V version with cable | plentyShop LTS
E14 to GU4 / GU5.3 adapter
Finding your way around lamp fittings | dmLights Blog
MR16 (GU5.3) MR11 (GU4) & G4 Low Voltage Bulb Holder - BrightOn LED lighting