Don't know why .us is not available through Namejet, I don't have any experience with this extension.
However, what I do know is that generally if a domain is already in pendingdelete stage, then it doesn't matter who the "partner" is. The domain will be available to reg by any dropcatcher when it actually drops.
The best scenario would have been to backorder/participate in the pre-drop auction at the partner after the domain expired. At this point, I think you will need to backorder at all the major dropcatchers if you really want it.