I love mine on my 2018 Gen 3, so not parting with it, I only use it on the road but I like that it separates rebound and compression on the front end - the feeling from the front end for me was transformative. I bought mine several years ago from a dealer in Reigate who seem to have now disappeared!
But if it is any help, it was an Alpha Racing part number 7470HP4A00 it came with a fitting kit - looking at the Alpha Racing site now, they only list 2D potentiometers for the Gen 4 K67/66 machines not the K46 (Gen 3). Perhaps you might contact them directly here and ask them if they can help you?
Just found one at Fortis Racing here for ?435 and they claim it is in stock