Return all subclasses that are admin registered.

def get_content_models(self):
        """ Return all subclasses that are admin registered. """
        models = []

        for model in self.concrete_model.get_content_models():
            try:
                admin_url(model, "add")
            except NoReverseMatch:
                continue
            else:
                setattr(model, "meta_verbose_name", model._meta.verbose_name)
                setattr(model, "add_url", admin_url(model, "add"))
                models.append(model)

        return models