I don't know but the question interested me, so I googled a little, and found one place to start. The CBOE FLEX facility allows participants to ask for option quotes for up to 15 years. They apparently also do a "mark" of existent positions here
, and I can see up to Dec 2026. So you could extract some implied vols from those. What I would suggest is that you follow up with the CBOE to learn about their marking procedure and, if you find out anything interesting, please post what you learned.