All Configurable Options Module for Magento by outer/edge
This module will show all available options that are available for a configurable product, regardless of stock levels for the associated products. For example, if you have a clothing item available in three sizes - Small, Medium and Large, and the Small size is out of stock, Magento would not show this option. However, with this module all options will be displayed, but out of stock items will be disabled.
To show out of stock options in the configurable product, enable(set to'yes') "Display Out of Stock Products" in Stores->Settings->Configuration->Catalogue->Inventory-> Stock Options