I bought mine on ebay
https://www.ebay.com/p/Niles-Spk-1-Black-Speaker-Level-A-b-Switcher/1301529465
If you need to switching sub-woofer:
https://www.ebay.com/itm/Niles-Audio-AVS-2-Line-Level-A-B-Switcher/323424938106?hash=item4b4da0e87a:...
Or combination of both:
https://www.smarthome.com/niles-audio-sas-1-combination-speaker-level-a-b-switching-system.html
https://www.ebay.com/p/Niles-Spk-1-Black-Speaker-Level-A-b-Switcher/1301529465
If you need to switching sub-woofer:
https://www.ebay.com/itm/Niles-Audio-AVS-2-Line-Level-A-B-Switcher/323424938106?hash=item4b4da0e87a:...
Or combination of both:
https://www.smarthome.com/niles-audio-sas-1-combination-speaker-level-a-b-switching-system.html