is there a guide of this anywhere?
Not that I know of, because the process is quite different from a site to another...
What you generally wanna do is :
- open the devs panel on your browser
- locate the game's html element through the highlighting and find the iframe pointing to the game.html
- open that link, this should give you only the game
- go to Sources and look for game.html, you can see some .js files and a .json listed in here
- the json will list the unityweb files and their relative address
- now with all that knowledge, reproduce the folder layout by downloading these files to a local folder
Be aware that unityweb won't run in local on your browser though, and that reproducing a webpage using files that are hidden to you to begin with might infringe several laws (even though, you already got access to those files at some point by displaying the page, dunno...), but I can't be sure of it, I'm a dev, not a lawyer.