We typically add custom post types via the functions.php file.

If you’re following this route, you can use any “out of the box” Dash Icons with one line of extra code in your register function.

register_post_type('attorneys', array(
	'label' => __('Attorneys'),
	'singular_label' => __('Attorney'),
	'public' => true,
	'show_ui' => true,
	'capability_type' => 'post',
	'hierarchical' => false,
	'rewrite' => true,
	'query_var' => false,
	'has_archive' => false,
  'menu_icon' => 'dashicons-buddicons-buddypress-logo',
	'supports' => array('title', 'editor', 'thumbnail')
));

You can find all the options here:

Dashicons

The result?