Footswitch Box - Marshall, Two Button (Channel, Reverb) | Amplified Parts
A special mini amp channel switcher/FX loop pedal (When you actually only use 1 of the 2 functions and the other is always on or off) Details in comments. : r/diypedals
Hot Box ABY-330 Micro A-B-Y channel switch pedal | Reverb
Footswitch - Channel Switching, Single Button with LED - MESA/Boogie