WooCommerce Stock Management with other Services | http://www.ibenic.com/woocommerce-stock-management-services

hook.php

<?php

// woocommerce/includes/abstracts/abstract-wc-product.php

/**
 * Returns number of items available for sale.
 *
 * @return int
 */
public function get_stock_quantity() {
  return apply_filters( 'woocommerce_get_stock_quantity', $this->managing_stock() ? wc_stock_amount( $this->stock ) : null, $this );
}

hooking.php

<?php

add_filter( 'woocommerce_get_stock_quantity', 'woodev_stock_get_stock_quantity', 10, 2 );

product_field.php

<?php

add_action( 'woocommerce_product_options_stock_fields', 'woodev_stock_product_service_field' );

product_save.php

<?php

add_action( 'woocommerce_process_product_meta', 'woodev_stock_product_service_field_save' );