Try the yellow pages for stables. Stud farms. etc
Phone up and ask them if they pay to have their stable sweepings placed in landfill. Then offer to accept it free.
It will take a while for it to rot down but once started........
We built a manure bin on our site about 10 years ago. Got a grant to do it too. The farmer brings us stuff regularly and it is left in the bin in stages.
When the bin gets full he sees if any one wants him to take the oldest to their plot. Then delivers the rotted stuff to make space. Because he wants to get rid of it more than we need it now.
You wont be able to use it straight away but it is well worth organising. I would say that it takes about a year to get it well rotted enough.
The horses are sometimes outdoors this time of year, (which is where they do their business) so you may get a lot delivered in the winter when they are indoors more.
UC no one is going to tell you where they get theirs 'cos they want it all.
Try free cycle in your area and put 'wanted' stable sweepings for manure bin. Will accept delivery. (never offer to collect unless you have to)
