Look for reputable websites that offer the IPA file. Be wary of sites requiring excessive personal information or those with dubious reputations.
For those who never owned the game or want to archive it, several community repositories host the original IPA files: Call Of Duty Black Ops Zombies Ipa Download
The original Black Ops Zombies was a 32-bit app. Since iOS 11, Apple dropped 32-bit support entirely. That means: Look for reputable websites that offer the IPA file