there are several breeders on this forum and there may even be one near you, depending on what part of the country you're in
Scott Felzer seems to be the biggest commercial garter breeder outside this forum, and he has excellent snakes, but if you're going for a pet, I highly recommend getting one from a small breeder here on the forum, who gives them a little more individualized attention early on, and possibly even gets them feeding on f/t pinks