Can you get your hands on some Calcium Chloride locally ? Maybe one of us out your way can get you some ?
All you need right now is 2 cups to mix with RO for a total of 3,785ml. Don't add it to a gallon, but rather mix it 'till dissolved in about 1/2 gallon, then add enough RO to make a gallon.
Once you have that gallon mixed, use
this online calculator to help with the dosing amount needed.
My thought is to use the chloride to get your calcium up, and then carry on with what you've been doing to maintain the big 3.
I've never used Kalk or C-Balance and don't want to lead you in the wrong direction, so hopefully someone who has will speak up ...