As far as where to find them: some grocery stores carry them, but odds are you'll find the "popular" flavors which are nearly always limited to vanilla, almond or hazelnut.

If you can't find a supplier near you, go to your favorite coffee shop or espresso stand and ask them where they buy their supplies. Odds are most small stands shop at a foodservice or restaurant supply store and you could go there and choose to your heart's content.