Here is a 3:1 stereo XLR switcher you can pick up at Amazon. Be aware during your search to inquire about audio clicks and pops during switching. I’ve heard that such can be pretty loud.
Nobsound Little Bear 3(1)-IN-1(3)-OUT XLR Balance Stereo Audio Switcher Passive Selector Splitter Box
Nobsound Little Bear 3(1)-IN-1(3)-OUT XLR Balance Stereo Audio Switcher Passive Selector Splitter Box