Sorry, 2018 is no longer supported.
I still see the 2018 version in my downloads folder in my Turbotax account, and I believe the download is automatically updated to the most recent patch. So Turbotax has it, even though they officially don't support it. You would have to call customer support and see if they will do a deal for you.
https://ttlc.intuit.com/turbotax-support/en-us/help-article/account-management/turbotax-phone-number...
