Widget to display custom taxonomy tag cloud

Don’t know of any but you can easily create your own:

<?php 
add_action("widgets_init", array('Widget_Custom_tax_tag_cloud', 'register'));
class Widget_Custom_tax_tag_cloud {
    function control(){
        echo 'No control panel';
    }
    function widget($args){
        echo $args['before_widget'];
        echo $args['before_title'] . 'Your widget title' . $args['after_title'];
        $cloud_args = array('taxonomy' => 'Your taxonomy here');
        wp_tag_cloud( $cloud_args ); 
        echo $args['after_widget'];
    }
    function register(){
        register_sidebar_widget('Widget name', array('Widget_Custom_tax_tag_cloud', 'widget'));
        register_widget_control('Widget name', array('Widget_Custom_tax_tag_cloud', 'control'));
    }
}
?>

just change : ‘Your widget title’ with your title and Your ‘taxonomy here’ with the name of your taxonomy.

you can change the look and feel by passing more arguments in the $cloud_args from the large list in the codex

Hope this helps.