Drupal/Ubercart by itself can't restrict access to certain nodes by itself. To restrict access to certain nodes you'd have to use the Drupal core taxonomy module and a module like TAC lite or Taxonomy Access Control. Once enabled, you can add a taxonomy to nodes that can only be viewed by a certain role that you create. With that role and taxonomy in place, you can start selling the Role you created with the Ubercart Roles module.