If you are referring to "jet"—a black gemstone made of fossilized wood—you can find extra-long "opera length" necklaces and large raw specimens at these retailers:
: Specializes in handcrafted Whitby Jet necklaces and pendants inspired by the Yorkshire heritage. Specialized "Long" Aircraft
: A leading platform for jet aircraft with over 1,200 active listings, including large and long-range models.
($350) and ($210).