While not official Microsoft mirrors, sites like the Internet Archive host community-preserved versions of the original media.

: Active members can log in at my.visualstudio.com to search for and download the Windows 8.1 ISO with official SHA-1 hashes for security verification.

There are many websites claiming to offer ISO downloads, but downloading from third-party "warez" sites is dangerous. The files are often infected with malware or modified to include bloatware.

The "full story" on downloading a Windows 8.1 32-bit ISO has changed significantly because

(still offers Windows 8.1):

Use the official Microsoft Media Creation Tool with your valid product key. If the tool fails, use a verified open-source downloader from GitHub that fetches Microsoft’s own servers.

: Mainstream support ended in 2018, extended support ended January 10, 2023. Microsoft no longer provides security updates.