In the past I have seen where sites will have online applications for potential models. They'll usually ask for basic information about them and usually some pictures, too. I have also seen where some actually put ads in their local newspapers (that's what some say on their sites, anyway).
I am not for sure, but I think some producers actually visit college campuses and ask around for potential models and/or put up fliers. If you could muster up the nerve to do that, you might get some good results.
Hope this helps some.