Sidebar Select Meta Box for cmb_meta_boxes

sidebar_select.php

<?php
/**
 * Adds a new sidebar_select field type to CMB Metaboxes
 *
 * Builds the select box from all registered sidebars.  
 * Use in themes to create per page or post layout options without having to create new templates
 *
 * @see https://github.com/jaredatch/Custom-Metaboxes-and-Fields-for-WordPress.git
 *
 */

if ( is_admin() ) {  // Optional is_admin check.  I only include the metabox class on the admin side.
	add_action( 'cmb_render_sidebar_select', 'wpu_sidebar_select', 10, 2 );
	add_filter( 'cmb_validate_sidebar_select', 'wpu_validate_sidebar_select' );
}

/**
 * Adds a custom field type to the meta box class
 *
 * @param array $field Your new field
 * @param mixed $meta Current saved meta_value for the key
 */
function wpu_sidebar_select( $field, $meta ) {
	$sidebars = $GLOBALS['wp_registered_sidebars'];
	echo '<select name="', $field['id'], '" id="', $field['id'], '">';
	    foreach ($sidebars as $option) {
	    echo '<option value="', $option['id'], '"', $meta == $option['id'] ? ' selected="selected"' : '', '>', $option['name'], '</option>';
	    }
	echo '</select>';
	echo '<p class="cmb_metabox_description">', $field['desc'], '</p>';
}

/**
 * Validation function for sidebar_select meta box field
 *
 * @param string $new The new value to validate before saving
 * @return bool|string If validates returns the value
 */
function wpu_validate_sidebar_select( $new ) {
	$sidebars = $GLOBALS['wp_registered_sidebars'];
		if ( !array_key_exists( $new, (array)$sidebars ) ) $new ='';
		return $new;
}

if using smof or options framework by devin then you can use the following in the options file (function.options.php in smof) to call in the registered sidebars as options,

            $of_sidebars = array();
    $of_sidebars_obj = $GLOBALS['wp_registered_sidebars'];
    foreach ($of_sidebars_obj as $option)
    {
        $of_sidebars[$option['id']] = $option['name'];

    }
    $sidebars_tmp = array_unshift($of_sidebars, "Select a sidebar:");

then in your chosen field type add "options" => $of_sidebars,