Official in-game map downloads do exist. Custom maps are community-made and available on third-party sites:
Turbo Dismount is a physics-driven wreckfest that invites players to design glorious vehicular disasters and watch them unfold. If you’re looking to add custom maps or download community-made levels, this short guide walks you through the safest, fastest ways to find and install maps for Turbo Dismount. turbo dismount map download