Recommendations for a good USED steel gravel bike?

I'm aware there are lots of options, but what I don't know is what's most commonly available on the used market. And unfortunately, FB marketplace and its sellers are mostly terrible, so searching for steel bikes will turn up lots of alloy and carbon frames. Almost no one actually fills in the material field, so filtering with that is useless.

What I'm interested in is whether there are any mainstream-enough steel gravel bikes/frames that I'd be likely to be able to find them used. Like which frames, specifically, should I be searching for? Bonus points if it's a UDH frame, although that's probably asking too much unless buying new.

(Please don't try to convince me alloy, carbon, or Ti is better. I have a carbon race bike, I want steel specifically for a "beater/winter/apocalypse" bike and something I can mess around and tinker with over time. For environmental and financial reasons I'd rather find something used.)