@robincnn makes them to order depending on your needs which is why they show up as 'out of stock' on his site. Just message him and he will build them. You can also just get a simple 2"x4" junction box at home depot and drill a few holes. They have all the parts you need for the box in the same section at home depot. I bought one from Robin and then made one myself. One side for AC and one side for DC. Other than the boxes and inserts for the holes you drill all you need are wago connectors which you can google, they are sold everywhere.
edit: just noticed they aren't on his website so you might have to just build them yourself. Trust me it's easy. Just a box that holds your wago's and potentiometer.