I'm not too sure what you mean by "co-ops". There are some "alliances" that are doing well for their members, US Premium Beef, Nebraska Corn Fed Beef are two. Future Beef just went broke, but another group is trying to buy their plant. Getting a large group of independent cattlemen to agree on genetics, management, and marketing is a tough thing to do. And if you are looking to create your own branded beef line, you need a lot of pounds of beef all year long or the supermarkets won't even talk to you. There are several groups working on it, though. I think we'll see more of it in years to come.
The Drovers site used to have a list of active alliances with some info on requirements and contacts. You might look at the site and see if it's still there. A beef animal is probably owned by at least four different people, producer, backgrounder/stocker, feedlot and packer. They all add value and make some money on the calf. It seems to me if a group can get together and keep more of that money for the producer, we'd be better off. The beef industry has changed a lot the last five years and more to come. Here's the Drover site: