I posted once and it isn't showing, but try:

Noble Foundation - Ardmore, Oklahoma

Here is a link that might be useful: Noble

Dale, I think the Noble Foundation in southern Oklahoma has done a lot of work on Elbon Rye.

I buy Elbon Rye at the farmers co-op. The cost depend on supply and demand, I have paid from $13.00 to 25.00 per 50# bag. You can plant it alone or with something else.
I plant it alone because it is hard enough till in that way, if I sow vetch in with it I think it is a better cover crop, but even harder to till in.

If you cant find Elbon, there are others that may be as good and even a little cheaper. I think Elbon heads out a little later, but for me that does not matter because I till it in long before then.

Larry

I could be wrong but I think any cereal rye will work.

It does it's work when it is tilled under in the spring. As the green leaves decompose it kills the nematodes the way I understand it.