You should be able to get poultry litter,horse manure and maybe feedlot cleanings. I've found that horse manure,since it is mixed with plenty of bedding,is great even without anything else mixed in. I've spread it straight on the fields in winter using my manure spreader and have also piled it up and then spread after it sat for 3-6 months. I've never done a formal compost pile with turning but my piles of horse manure have always made fine compost and I was able to turn 40 acres of clay with sparse weeds to,lush Bermuda using this method and only the seeds from the manure and hay used to seed the pasture.
I currently don't have a large place,just a small garden and 1.5 acres for the horses. I do harrow their pasture and that,along with scraps from the round bales,adds a great amount of organic matter to the pasture. I pile the stall cleanings up and use it as my compost,adding leaf mold and worm castings. Btw,the horse manure straight is like worm crack.
The neighbor has a huge (maybe 2,000 acres?) of crop land and he piles a mountain of turkey litter up all winter,delivered by semi. In the spring they spread it on the fields on top of the winter oats. The oats grow a month or two longer and and then get turned under so they can plant. They also rotate crops,using either soy or peanuts,then alternating with cotton or corn.
For something large scale I think cover crops are key,then hauling in huge amounts of manure,letting it sit in a pile a few months and spreading it.
We have sandy soil here so the farmers all use this method. It also works on clay,which I've experienced in OK,AZ,CO and WY.