We ran into the same dilemma after having been 'excluded' from Lassen Park, and then running down H-395. AND, guess what, NO alternative state parks, and mostly full private CGs, who jumped right on the bandwagon and raised rates.
In any event - we found a couple NF campgrounds still operating, and with staff. But, staff was paid by 'vendors', concessionaires, who were remaining open simply to collect revenue as long as possible and allowing travelers to stay on a pay-one-day-at-a-time basis.
When we ran out of those, we had to stay twice in hotels since we're 3000 miles from home. We plan to send a note of explanation with a bill for those nights to congress (Minus the two $8 camping fees we would have paid), once it opens of course, along with a copy of our senior "America the Beautiful" pass. Once congress opens again, and pays the bill, we'll find some 'still-open' nature organization and give it.
We will also send a photo of the "This is your park, keep it clean" sign.