Now that SQL Server 2005 is end of life (since Apr 12 2016), it is time to upgrade your SQL Server 2005 instances if you haven’t already to get support from Microsoft.
There are several upgrade options available. Please see this page for more information.
Also, if you are looking for the last service pack for SQL Server 2005 (namely SP4) which is the minimum required version to upgrade to SQL Server 2014, you can find it in the Microsoft Update Catalog.
In the catalog search results, select the right package (for e.g. “Microsoft SQL Server 2005 Service Pack 4 (KB2463332)”) and click Add.
Then click on “view basket” and then Download to download the package.