EDIT: for some context on the problems this creates
The science is clear that fast-growing chickens like the Ross 308 are doomed by their genetics. These have been engineered to grow so incredibly fast, and their bodies just cannot handle it.”
Jackson said secret filming at broiler farms supplying big supermarkets has shown birds struggling to walk or collapsing under their own weight, or dying from heart failure, and dead birds were filmed lying among the flocks.
[...]
Andrew Knight, a professor of animal welfare and ethics at the University of Winchester, said: “With these really rapid growth rates, it can be difficult for the heart and circulatory system to keep up with the expanding body mass. A proportion of these animals suffer from heart failure. It’s also difficult for the bones, ligaments and tendons to keep up with the rapidly increasing body mass, meaning that a proportion of these birds become severely lame [inability to walk properly].”
And that quote only lists just some of the health problems they face. There's a ton of other problems too
The places one get chickens from are likely going to be the same or similar to the common commercial breeds.
It's also worth noting that domesticated breeds of egg-laying chickens haven't been spared either :( They have been selected to lay so many eggs that it harms their bone health. It takes a lot of calcium to make eggs, so naturally they don't lay them as much. In the wild, they would also often eat their own unfertilized eggs to recover the calcium too. I've read that a fair number of animal sanctuaries actually give them medications to lower their rate of egg laying and let them eat their own eggs to recover that calcium
https://ourworldindata.org/do-better-cages-or-cage-free-environments-really-improve-the-lives-of-hens
Ideal egg breed hen would be akin to a termite queen, it seems