There are lots of them on Gunbroker, thats where I got mine a couple years ago when the 10 Gauge nostalgia bug bit me. My dad had one when I was younger and I borrowed it for duck hunting a few times. I developed a saying after using it. "When you pull the trigger, something dies." What a cannon! That gun went away long ago and so I wanted to get another.
I use it for pass shooting geese while standing on my back lawn. The H&R Model 176, 36" barrel. I just checked Gunbroker, there is a Model 176 on there right now.
You know, I got some turkey loads for it, just to test it out, and HOLY COW do they kick!!!!! And you don't get anything good for all the recoil either, at least from my gun, the pattern was NOT impressive! Drops geese nicely though from way up.
Good luck in your search!