Mimicing Custom Themes

I have a few WP sites and have always used the provided free themes. I am now creating a site for a friend who wants to mimic THIS site. After reading the source code I see that it’s a custom theme but my friend wants something as close to this as possible.

Any advice to recreating this in a theme creating platform? Is there a way to basically copy a custom theme that’s not available to download?

Any advice is greatly appreciated.