This is where I keep my urdf files for experiments.
The urdf file that I use in my custom gym environments is the 8-link octopus arm (make sure to add them to your pybullet datapath): https://github.com/roman-aguilera/romans_urdf_files/blob/master/octopus_files/python_scripts_edit_urdf/octopus_generated_8_links.urdf
The custom gym environments that I made are found here: https://github.com/roman-aguilera/romans_pybullet_gym_envs