You can buy them from supermarkets and health food stores. They are cheap amd I don't think it matters whether they are golden or brown. The fresher the better so vacuum packed is good. The taste does vary so try a few. And yes, soak overnight and chew them in the morning, I find a 3-4 teaspoons is plenty.
Gave it a break because I got forgetful, but the benefit to my day reminds me to do it.