Build your own USB C to 3.5mm adaptor DIY Tutorial - YouTube
Amazon.com: Devinal USB C to RCA Audio Cable, Type C to Dual RCA/Phono TRS Stereo Cord Adapter Y Splitter for Smartphone, Tablet, Laptop Link Amplifier, Mixing Console Mixer, Speaker, 6.6 Feet :
USBC to AUX Adapter | Scosche
SpeaKa Professional AV Konverter [USB - Phono] 648 x 480 Pixel | Conradelektronik.dk