For specific builds and older sub-versions, you can navigate the directory structure at bitcoincore.org/bin/, which hosts binaries for various operating systems.
For "ancient" versions (pre-0.10.0) that may no longer be on official servers, community members often point to The Internet Archive or Satoshi's original source code. Common Use Cases for Older Versions Releases - Bitcoin Core bitcoin core old version download
You should only download legacy Bitcoin software from official repositories to avoid malware and "backdoored" clients. For specific builds and older sub-versions, you can