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?
Yes.
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.")
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8\$\begingroup\$ +1 for not only giving an answer, but also providing a solution for how to obtain the information for similar questions. \$\endgroup\$ – linksassin♦ Mar 13 '19 at 1:12