Not sure where you are located but is something like this really that much more than Aliexpress?
https://www.amazon.com/CableWholesale-Stereo-Coupler-Female-30ST-STFF/dp/B000I963FE/ref=sr_1_2?crid=3JK0LTUCTXVLJ&keywords=3.5mm+coupler&qid=1555937336&s=gateway&sprefix=3.5mm+co%2Caps%2C171&sr=8-2