Since no one has responded to this I will give you my opinion. I am by no means an expert.

You can search on Local harvest.

Finding clean manure will be nearly impossible. Even though the animal owner may use organic feed, without antibiotics or hormones, if they purchase hay, the hay likely has herbicides in it. A lot of those owners have no idea that persistent herbicides may be in their hay.

This article tells you how to test manure and compost (towards the bottom). http://smallfarms.oregonstate.edu/sfn/f09Herbicide

Alternatives might be cover cropping, your own compost, worm castings (those are pure gold). You don't mention rabbit manure in your post, it is wonderful fertilizer.

Articles that might be useful:

Organic Fertilizer

Green manure
Alfalfa

Milk and mollasses

Feed your soil

Grow fertilizer

Thank you for your reply. I just read the article you recommend and it is excellent information! I used wheat straw mulch on my tomatoes and now I need to go test it for herbicides. I already do compost, cover cropping and no till gardening but I need more compost. All of your suggestions are very helpful!

I agree with Amy that you are unlikely to find anything that is 100% clean. Anyone who is raising their livestock on such a clean diet is likely to keep the manure for their own use on their own property because pure, clean compost is as valuable to gardeners as gold. There's just too many ways that persistent herbicides can "sneak" into manure nowadays, including via contaminated, bagged feed. I remember one case where contaminated manure/compost was traced back to bagged Purina horse feed that contained herbicide residue, but this didn't happen until hundreds of gardens already had been contaminated by the stuff after the herbicide residues had survived the horses' digestive tracts as well as the composting process.

The only way you'll ever have 100% clean compost or manure will be if it is produced on your own property and you do not use any inputs, like feed, that come from off your property. Unless you have 100% control over it, you cannot be sure it isn't contaminated.

The closest you will come to having safe manure or compost is to obtain the manure well in advance of the time you need to add it to your soil, compost it yourself if it is not already 100% composted and then test it yourself using the bioassay methods established to work for this testing purpose before you add it to the soil.

I haven't brought in any form of local animal manure since around 2003, preferring to make my own compost with material from our property instead. It is tons more work, but at least we do have acreage so I can gather tons and tons of leaves and grass clippings to use to make compost. I haven't even brought in any spoiled hay to use as mulch since 2010 or 2011. We have chickens but we do not feed them 100% organic grain, so I don't even use their manure/coop bedding in the compost pile that produces compost for my veggie garden. I compost it separately and use the finished compost in areas where I grow ornamentals.

If you do, by chance, contaminate your soil with herbicide residue, you can remediate it and eventually clean the residue out of your soil, a process which can take a year or two or even three or four depending on how high the herbicide residue in your soil is and depending also on the remediation methods used. I just prefer to not bring in anything from the outside that could put me in the position of having to do soil remediation in the first place.

The only manure I have brought onto our property in recent years has been a bagged 100% cow manure called Black Kow, and I don't use it very often any more. However, I've never had a contamination issue with it.

I just make compost nowadays mostly from grass clippings and tons of autumn leaves. If I need hay, I buy alfalfa hay because alfalfa is a broadleaf legume that cannot be treated with the kinds of herbicides that are the cause of persistent herbicide residue contamination. I am surrounded by horse and cattle ranches and our neighbors offer me manure all the time, and I decline it every time because all of them use purchased hay from time to time (especially in drought) and purchased hay is a common source of herbicide residue.

The days of gardeners being able to obtain truckloads of clean, herbicide-free manure are over and have been for a long time now. It is sad, but with the kinds of herbicides used nowadays, those days aren't coming back. Cover crops and green manure crops always have been important, but they are more important now than ever before because they are a great alternative to importing manure. It isn't too late (unless you are in extreme northern OK) to plant a winter cover crop like Elbon rye. Then, in late winter, you cut it and rototill it into your soil.