Since the style calls for native American hops, which there is no such thing, their native to China if memory serves, maybe this is a mythical beer and that's why a commercial version doesn't exist.
IMO, that is a misnomer in the guidelines.
There actually are "native American hops" for example Humulus lupulus neomexicanus
They are the wild common variety that occurred here prior to European settlement.
What I think they are talking about here are early American hops that may have become "naturalized".
Cluster is one of these varieties still around today...but it still has its origins from whatever the settlers brought over and it gradually became known as the classic American hop...for use in the Classic American Pilsner!