Brewing supply shops, and even the 'legal herb' vendors! They may be called 'cannabacea' if you buy them as 'legal herbs'.
Or you can look around if you have a local microbrewery/pub, most places around here anyway grow hops as an ornamental up the side of the building, and they are coming ripe at this time of year. They are pretty easy to grow, and hardy to at least zone 5, possibly even zone 4- I don't feel like looking it up, lol.