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 :
1/4 Mono Jack to 3.5mm Mono Jack Adapter - Audio Adapters - Interseries Adapters - Connectors & Adapters