One place is http://www.aquaticplantcentral.com/f...-checkers.html, where the 4 dKH solution is included, premixed with pH reagent (bromothymol blue). You could email that seller to ask about buying just the solution.

Here is a place to buy the 4dKH water. http://www.aquaticplantcentral.com/f...standards.html. You could email the seller and ask if he sells it premixed with pH indicator reagent.