The Eclipse doesn’t require a special aux switch. Any aux switch should work fine.

There are some details for making an 3-button aux switch in a thread here: https://www.eventideaudio.com/forums/topic/i-am-making-my-own-3-way-aux-switch/

Otherwise, you should be able to find some simple options searching for “DIY aux switch”.

There is a calibration menu in the settings that will let you confirm if your switch is working or not.