Where can I get well rotted manure from?

[UnrequitedSkink]

I've dug up the front lawn and turned it over, and apparently (according to what I've been reading today) I need to top dress it with well rotted manure to help it break down over the winter. (With a view to landscaping it in the Spring). Any ideas where I can get some from?

Riding stables usually have tons which they are happy for you to have so long as you bag it up yourself. Empty rice sacks from chinese and indian takeaways/restaurants are good as they are very strong and big but not too big.