I second the "all asian grocery stores have it" comment. Check by the other fresh greens up top and it won't even be in a moldy little box, it'll be in a little bundle like the parsley. Depending on where you are, you can also check a historical site that has a garden, a plant nursery, or farmer's market. Peppermint is super easy to grow and tends to take over. Oh, but don't bother with Home Depot or Lowe's for herbs after the 4th of July. Actually, don't bother with them at all since their herbs have been touched by everyone passing through the store. Would you really want to use an herb that EVERYONE has crushed, sniffed, dropped, and sneezed on in something you were going to eat?!!