I'm not sure about where to get allen screws so small, but you can contact H-Fit to see if they'll be able to get you some spares. I also don't have a problem with it "hitting" in 1st and 3rd? Could you perhaps take more pictures and maybe ask H-Fit about it?
Cable A is easiest to take out if you have a crescent wrench for leverage and gently turn it counter clockwise.
