Man I'd do some google searchs. I cant remember where but id found this one site that had models from every sci-fi genre out there. Everything was divided into movie/show,ship,charmater,sets....
It was quite extensive and I know I'd gotten it from google...I was testing flying animations in max and used ties coming outta a star destroyer. As I remember these are all very high poly versions and I had to wait till I gotten a new graphics card to test casue the Star Destroyer had so many polys, it made my comp crawl.
Good luck.
PS: Lucas Arts/ILM is really resonable when it comes to fan art/projects....long as your not making money off their name, heck they probly got a section of their site where they would display your work...provided it was good enough.......some fan based films/art/other is realllllllllyyyyyy good