How to get links for material shaders (.mdl) and usd assests (.usd)

I am generating synthetic data in which I change the background material of a plane randomly and add random props into the scene.

I have 3 questions.

  1. Where to get all the links of .mdl material shaders so that I can just cycle through them. Currently I am loading each material into stage and getting url from property window of the shader.

  2. Similarly where to get the .usd url for nvidia assests. Currently I load them into stage and get links from property tabs. Its tedious work to get each prop link . I would like to have randomly put 20-30 props in the scene.

  3. Is there any code tutorial how to randomly scatter 20-30 prop assests in a scene without collisions.