You could try:
This is the USDA seed bank for wild hops. They don't give out seeds for the standard varieties like Cascade. I think because the seeds are open pollinated and they could not guarantee who the father plant would be. These seeds pretty much seem to be seeds for wild North American varieties.
They also have rhizomes and in-vitro plant cultures:
These plants they can guarantee the lineage for. They typically will not give you a rhizome for something that is commercially available. Also I have had mixed luck with getting free stuff from the USDA. Half of the times they send me something and the other half of the times they make a lame excuse about why they can't send something. They will say that they don't send stuff to home gardeners or they don't send stuff that is already commercially available.
I have never asked for anything hop related from the USDA so I don't know how friendly the staff in Oregon is. If anybody does go this route please post back whether they were successful or not. I am going to wait till March and ask for rhizomes of something like Sorachi Ace since you can't buy those rhizomes.
I may ask for some wild North American seeds so I can breed them with some of the known varieties so I can create something new.