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The 3D Rex was obtainable in Season 33: "Jurassic" by reaching level 4.
3D Rex is the newest L4 reward from the season. Its comparable to other 250K furniture such as (but not limited to) Neon Vein Wall-Art, Hero Zapper or Fabulous Sign, and is very much interchangeable with those (and other 250K items aswell).
Supply is widely distributed — no single holder owns enough to register as a hoarder.