I have had excellent results with Albert Lea Seeds in MN.
http://www.alseed.com
They have both Organic and non-organic varieties and many pre-mixed green manure and forage mixes.
I have used their nitromax mix of oats, peas, and tillage radishes and it is awesome. Seed it in August and it will totally winter kill. The daikon radishes get huge and melt away in the spring.
I also used one of their pasture mixes for increased diversity in my annual grazing lanes and will have a better idea of how that is working next year. This mix includes:
20% BG34 Barenbrug Perennial Ryegrass
15% Milkway Fescue Blend
15% Ginger Grazing Bluegrass
5% Birdsfoot Trefoil*
2.5% Alice White Clover 15% Smooth Bromegrass*
15% Spring Green Festulolium
10% Baridana Orchardgrass
2.5% Chicory*
All of their seed mixes are available in 50# bags for large scale use but if you call them they will happily put 5#'s in a bag and send it out with minimal price per pound difference.
Excellent selection, commercial level prices and super easy to work with. Plus family owned and operated from Minnesota...