A bunch of galleries from people who upload .fbx models that i've checked and have cyberpunky/scifi/mecha models for download in them:
https://www.deviantart.com/grazekai/gallery
https://www.deviantart.com/flvck0/gallery/all
https://www.deviantart.com/lezisell/gallery/all
https://www.deviantart.com/rotten-eyed/gallery/all
https://www.deviantart.com/g1pno/gallery/all
https://www.deviantart.com/vlthar/gallery
https://www.deviantart.com/sticklove/gallery/