Amazon.com: CableWholesale 1/4 inch Mono Phono to Dual RCA Adapter, 1/4 Mono Male to Dual RCA Female, 6 inch : Electronics
0.5ft (0.15m) Value Series™ One RCA Mono Male to Two RCA Stereo Male Y-Cable | Audio Adapters and Couplers | Adapters and Couplers | Audio Video
Mono Audio Adapter - 3.5mm Plug to RCA Jack | Computer Cable Store
ADA-10170 Audio Adapter 1/4" (6.35mm) Mono Male to RCA Female | Kobe Trading Company, Inc.
Stereo to mono adapter for Anti-Mode 8033
Amazon.com: C2G Legrand RCA Male to RCA Female Signal Splitter Cable, Black RCA to RCA Splitter, 6 Inch Audio Stereo Y-Cable, 26 AWG Audio Signal Converter Cable, 1 Count, C2G 03177 : Electronics