The catoblepas appeared in various monster manuals throughout D&D's editions. Have WotC published stats for it in a D&D 5th edition product yet? If so, which?
The catoblepas was published in Volo's Guide to Monsters (page 129) for 5e. It is available here on D&D Beyond behind a paywall that requires purchasing the content.
Note that you can also use D&D Beyond to search monsters that are available in official D&D publications. You will be able to see the search results including the monster's name, type, CR, and publication source even if the full stat block is behind a paywall. (For example, here are the search results for "catoblepas.")