Contact your local garden center or nursery. Experts there will be able to tell you if they have any stevia plants in stock or if any other local retailers may. If not, be sure to inquire about special ordering one. Most garden centers have out-of-state or international contacts.
Navigate online to locate herbal retailers. Be sure to compare prices and make sure that they provide shipping to your area. It is shrewd to research online retailers prior to giving any sensitive information like credit card numbers over the web; a telltale sign of reliability is a street address or telephone number. Stevia is native to South America, around Paraguay and Brazil, so looking for retailers in that area may give you access to the highest quality plants.
Visit your local health food store or cooperative. Chances are, these establishments sell stevia liquid extract or powder. Perhaps an employee can give you some advice on where to obtain a stevia plant.
Plant the seeds or cuttings if you happen to obtain them. Stevia is a finicky plant to grow. The best conditions are year-round temperatures of over 65 degrees F, sandy, well-drained neutral soil, full sun and ample fertilizers that have a relatively low nitrogen content. They do well in pots if you live in a less-than-ideal climate.