Reports / export spreadsheet?

Thanks Pieter. I will have a go.

Of course!

I installed WooCommerce Simply Order Export and used the following code (adapted from this support post) to add ‘Source’ to the exported spreadsheet:

//Extra fields on CSV export
function wpg_add_columns($cols) {
	$cols['source'] = __('Source', 'themedomain');
	return $cols;
}
add_filter('wpg_order_columns', 'wpg_add_columns');

function wpg_add_fields($settings) {
    $settings['source'] = array(
								'name' => __( 'Source', 'themedomain' ),
								'type' => 'checkbox',
								'desc' => __( 'Source', 'themedomain' ),
								'id'   => 'source'
							);
	return $settings;
}
add_filter('wc_settings_tab_order_export', 'wpg_add_fields');

function csv_write( &$csv, $od, $field ) {
	switch( $field ) {
		case 'source':
				$customfield = get_post_meta( $od->id, 'source', true );
			array_push( $csv, $customfield );
		break;
		default :
			break;
	}
}
add_action('wpg_add_values_to_csv', 'csv_write', 10, 3);