The vigor in growth you see in the meat kings, the cornish cross or rangers is the fact that they are hybrids. Their fast growth and oversized muscle is achieved through selective breeding, not hormones or genetic modification. There's a boatload of misinformation out there.
You can order meat chickens from pretty much anywhere. TSC have them every year as well as red rangers. Your local feed stores will get them as well. Start talking to your feed store guy around Feb/Mar time frame and you'll probably be able to special order what you want for their spring run at no extra cost. They may or may not tell you the hatchery they order from.
You can order from any online hatchery pretty much anytime, but you'll want to pick the milder seasons for the least stressful shipping. You'll also want to call ahead to the post office to let them know exactly when they should expect them. My post office was willing to call me the moment they arrived and allowed me to come and pick them up during off hours. The chicks were all healthy when they arrived.
If you want to stick with dual purpose birds, New Hampshires, White Rocks, and Delawares are a few that have a decent sized carcass in 16 weeks.
Edited by Nupe - 12/10/15 at 7:28am