If you can’t find a guest's contact detail easily, these approaches can help you.
Some podcasters provide their contact details in their show notes for any listener. This can make it easy to contact them.
Podcasters and other guests often have a website where they provide contact forms or list their contact details.
Most people have some form of social media account and often provide the details to the public. If you can find them (via a google search) you can either send them a public message or you may be able to send them a private or direct message.
Try searching for the podcast name and “email address” or “contact”. You can also try using “Site:” followed by the site URL and then “contact” or email, this can help you find details that have since been hidden.
*Or Bing it I suppose