I would get a small recently morphed froglet, which as other stated are very often sold by pet stores. Tadpoles die off mysteriously (for no reason), some times it's just genetics. The whole tadpole stage is just something I would avoid for a newcomer to keeping frogs since tadpoles have such special needs.

You can order from xenopusexpress.com but it's not cheap. I would personally make call around to pet stores around you and just widen out your search a bit.. They are legal in your state.