https://digitalexits.com/listings/
https://feinternational.com/buy-a-website/
https://www.sideprojectors.com/
https://quietlight.com/listings/
Another alternative is finding small niche websites and make an early proposal, and you can find leads in https://betalist.com or search on Twitter "We are shutting down" and phrases like this.
I have this experience looking at someone else doing so. I can tell you it was not fun. Do all your diligence about all the details that matter, trustworthy metrics, IP, real costs, and advertising history; don't trust so easily.
Another piece of advice is to start small, don't buy a 100.000 $us business, start with something less than 5.000 $us, and learn how to measure and reprovision costs; it's not always evident how to continue with an existing business.