Where to find good 3d models for printing

I need a man/knight statue for 3d printing but everything I have tried to find in the 3d warehouse needs so much fixing for it to be a solid group that it isn’t worth the time.

  1. Things need to be a solid on order to 3d print them… right?
  2. Is there a quick way to fix objects to be solid that I’m completly missing?
  3. Are there other better places than the 3d warehouse where I can find 3d models that are done such that they are a solid?