I am building some of them myself in Blender. Some I have downloaded from various free sites. But I have the same problem every time I try to import in .obj or .3ds format. When I build my own objects in Blender and save them in .3ds or .obj format I have that problem. When I save them in .dae format, they import with their textures intact, but some of the faces are reversed causing me to have to import them twice as described above.