I used to shoot exactly the way you did. Although being in LA, theres normally an alternative newspaper in your city. LA's is the LA Weekly. We'd put a post in there looking for models of all types and everyday I would be inundated with calls. I think the key with that was stating it was a "Playboy-style" shoot, it attracted some good looking girls. Also try
www.adultstaffing.com. You can get some potential girls from there as well.