Amazon.com: Roland GA-FC Foot Controller for GA-112 and GA-212 : Musical Instruments
Boss GAFC GA Foot Controller | MIDI Footswitches & Pedals - Mannys Music // Mannys Music
Boss GAFC GA Foot Controller Pedal | Mooloolaba Music
Haven't seen a lot of examples of boards that implement the GA-FC, so here's the one I just put together! (Also posted in r/guitarpedals) : r/BossKatana
How the Boss Katana 100 and Roland GA-FC Footswitch Work Together - YouTube