The only free model I have found is at the Sketchup Warehouse. I had this about a year ago and converted it using Babel3d. I had quite a reasonable conversion. See my posts re Spaceship Two. I could buy one at $149 but I won,t. If someone has the Sketchup model its worth adding a few polys to make it really good. Add an undercarriage etc, I could do the textures if anyone wishes.