Amazon.com: 3.5mm Stereo Male to Dual 3.5mm Mono Male Audio Cable, 1ft 3.5mm 1/8" TRS Male to 2 x 3.5mm 1/8" TS Male Y Breakout Cable Splitter Adapter for Headphone, Speaker :
Hosa Technology Stereo 3.5mm Female to Dual Mono 3.5mm YMM-492
Amazon.com: SPRODIO Single Stereo to Mono Converter, RCA L/R Audio Adapter Stereo to Mono summing Cable Adapter SC21 : Musical Instruments
Amazon.com: RFAdapter 3.5mm Mono to Stereo Adapter, 3 Pack 3.5mm 1/8" Mono Male Plug to 3.5mm 1/8" TRS Stereo Female Jack for Radio, Headphone : Everything Else
Adapt 2.5mm Stereo Plug to Larger Stereo 3.5mm Audio Jack
Stereo to Mono Adapter
3.5 Stereo to Mono Adapter – Rugged Radios
Amazon.com: Poyiccot 3.5mm to 1/4 Adapter Cable, 1/4 Mono to 3.5mm Stereo Adapter, 1/8 to 1/4 Splitter Cable, 3.5mm 1/8 TRS Female to Dual 6.35mm 1/4 TS Male Stereo to Mono Y Splitter Cable, 20cm/8inch