Restrict Content Pro – bbPress is a WordPress plugin that is an an add-on for the Restrict Content Pro plugin. It does not function on its own.
This plugin will add support for limiting bbPress forums and topics to paid subscribers only. It makes it exceptionally easy to have members-only forums
Restrict Content Pro is a subscription and premium content manager plugin for WordPress.
Plugin homepage: http://pippinsplugins.com/restrict-content-pro-premium-content-plugin/