1. Most of these models are offered by the community for installation into SFC3.
Most modellers have their own sites where you can download their models... mine is
www.STARYARDS.com (although it's down for another day or two)
2. I've heard people say it's possible to convert Milkshape 3d models into SFC3 models, but I don't have any concrete data on that. Milkshape is a cheap shareware 3d Modeller. (I think under $50) Itherwise, you're looking at 3dsMAX, and that's in the thousands...