It looks like we will be able to purchase Passes through Recreation.gov now (link below). I followed the link and under the "Need to Know" section it clearly states that both Weekly and Annual Passes are available but I could only find weekly passes to purchase. Maybe Annual Passes will become available soon. In any case, I think this is great news.
LINK: https://www.recreation.gov/activitypass/e210305d-b769-11eb-87ed-16dbf55c498d