Look in the classifieds. There are speaker mfgs who make them for about $100. The neutrik is best for music.
here's one
https://www.audiogon.com/listings/subwoofers-rel-speakon-cable-2018-01-07-home-theater
FWIW i've never used this one but have heard good reviews
here's one
https://www.audiogon.com/listings/subwoofers-rel-speakon-cable-2018-01-07-home-theater
FWIW i've never used this one but have heard good reviews