// Add New Variation Settings
add_filter( 'woocommerce_available_variation', 'load_variation_settings_fields' );
/**
 * Add custom fields for variations
 *
 */
function load_variation_settings_fields( $variations ) {

    // duplicate the line for each field
    $variations['text_field'] = get_post_meta( $variations[ 'variation_id' ], '_text_field', true );

    return $variations;
}