DK-20 was withdrawn in the US because of bad Dichroic fogging issues with US made Kodak films, it was made for a few years longer by Kodak Ltd in Europe as there was not a similar problem with British made Kodak films. It had to do with fall out from US atmospheric atomic tests affecting gelatin, and new techniques.
You can use Sodium Chloride instead of Thiocyanate, that was Kodak's approach with DK-20's replacement Microdo, then Microdol_X. Ilford released a data sheet
P10 on this before releasing Perceptol.
Ian