Hello,
Indeed, Microsoft SQL Server 2005 is an older version that has been out of mainstream support for a considerable amount of time. As you've noted, it's no longer available through official Microsoft channels, which can make obtaining a copy challenging.
There are third-party software archives websites that archive older software. Be extremely cautious when using these sites, as they may host malware or pirated copies. Always verify the integrity and legitimacy of the files before downloading and installing.
Best regards,
Karlie Weng