Make sure you have deep-integration set up inside your bbPress. Basically make sure WP is loaded.
You’ll need to add a call to the wp-footer action so the BuddyBar is loaded:
<?php wp_footer() ?>
Add that before the closing HTML tag in your bbPress template footer and the bar should show up.
You’ll also need to add a wp_head() call to inside the header of your template too, so that the CSS works:
<?php wp_head() ?>