Espresso powder is one of those ingredients that can be hard to find. Your typical supermarket grocery store probably does not stock it. It keeps very well, so if you are at a specialty store and see some, you should just buy a jar to have on hand. I also have to wonder who actually uses this stuff for drinking. It comes in such a little jar, the primary use must be as a food flavoring and not beverages.
My main uses of espresso powder are for truffles, caramels and ice creams. I've seen recipes that call for adding coffee grounds but unless you are looking for grain flecks, I would recommend espresso powder for a better flavoring. The smell is wonderful.