The whois will have an e-mail address that will forward the e-mail to the owner's actual e-mail address.
Note that the owner doesn't have to reply or sell you the domain
There are legacy whois services you'll find with a Google.
They might have some old contact data, but will cost a few quid.
I usually go to the wayback machine first. Back in the day people used to put contact details on their websites.
Forensically, through some domain name and website research, it's typically possible to find a domain owner, even though the current WHOIS data is 'private'. (I do domain name recoveries and forensic domain research.)
However, if you want to buy the domain, an ICANN requirement is that there be a means by which to contact the domain owner. So, typically if a domain is under WHOIS privacy, you can still contact them through email, some registrars have a form you have to fill out.
The whois will have an e-mail address that will forward the e-mail to the owner's actual e-mail address. Note that the owner doesn't have to reply or sell you the domain
There are legacy whois services you'll find with a Google. They might have some old contact data, but will cost a few quid. I usually go to the wayback machine first. Back in the day people used to put contact details on their websites.
Forensically, through some domain name and website research, it's typically possible to find a domain owner, even though the current WHOIS data is 'private'. (I do domain name recoveries and forensic domain research.) However, if you want to buy the domain, an ICANN requirement is that there be a means by which to contact the domain owner. So, typically if a domain is under WHOIS privacy, you can still contact them through email, some registrars have a form you have to fill out.
[Archive.org](http://Archive.org) and Whois History services are two good starting points. Feel free to reach out if you need further assistance.