This is for sale: https://forums.digitalpoint.com/threads/whmcs-owned-license.2876609/ You can buy it using Escrow.
I am just updating this thread to say that WHMCS officially STOPPED / BANNED the legal transfer of lifetime licenses around 2020? The official notice from whmcs is "The sale of Owned licenses was discontinued in 2016. And the ability to renew support and updates was discontinued in 2021." This means that from now on, anyone with a lifetime license can no longer pay for yearly updates! At best, if someone had a license in 2021, and had updates active for 12 months, the updates would have expired in 2022. The only way to "transfer" a license now, would be to include the email address and or domain name that owns the whmcs. But being 1 year out of date, with no yearly updates, it may be better to look for other software.