It is usually a targeted product, not all stores will carry it (unless it's post-Passover, and the warehouses are looking to clear out the KP stuff).

2 liter Coke will have a yellow cap with Hebrew writing on it. Cans will have KP on the bottom with the production code.

You'll have more success if you look in areas with a higher Jewish population, since that is who this product it targeted towards. I know we sold a bunch of it when I worked in northern NJ.