These are 100% legal and often more interesting than the original:
If you own Quake on Steam, the PAK files are already verified by the CDN. Here’s how to locate them: quake 1 pak files download verified
Ultimate Guide to Quake 1 PAK Files: Safe Downloads, Verification, and Installation These are 100% legal and often more interesting
Even with a good download, you might encounter errors. Here’s a troubleshooting table: quake 1 pak files download verified