I doubt that the people that might do such things, read here. In the meantime, maybe just browser popular paid web games here, and try to snoop in the code. If you can't but it is the type of game were the source would be unprotected, you have seen examples how to do or if and what to do.
I suspect https://itch.io/games/top-sellers/platform-web/store the ones with the highest incentive to make the web version somehow that you cannot simply download the source code, since they want to sell the download version.
To be honest, I was not even aware, that the source code of html5 games can be read. With comments and all. (That is what I meant above, there is no need to "buy" your game. Being able to play it, is enough to have access to something that your browser uses to run the game)