I don't think the threads are the same, but I'm not sure. I have a MIJ Long Dash DS-1 that's meant to have a SS, but has the standard black one. It doesn't fit too good.
i think Boss keeps these off the market on purpose. if the general public could get their hands on Silver Screws, i think there would be a lot more "super rare" PH-1s, CE-2s, NF-1s and other pedals that overlapped the silver screw/black screw era floating around.
but hopefully people would realize that paper-label pedals don't deserve a real silver screw (and ink-stamps should absolutely have one). You could probably contract someone to make a batch of the screws for you.. hmm..