If you have the specific required part number there is another vendor that may be worth a try. It is Paragon products. They primarily deal with Porsche and BMW. The resident Koni expert is Jason Burkett and is extremely knowledgable and helpful. I am not sure if his knowledge extends the entire Koni line but I bet he can find out.
For adjustment info on Konis see the Boss 302 Chassis Modification Guide available from many Mustang parts vendors. I set mine to the stage 2 setting plus 1/2 turn toward stiff in the rears. That is just firm enough to be well controlled around the cones yet won't launch me into orbit on a bump.