We have the same dilemma. A 1/2 dozen years ago, I was cutting up downed trees around here to get my firewood inventory up. Now, Shenandoah National Park won't let me carry firewood into the park.......even though I live less than 20 miles from the boundary. If the ash borer were here, it would be in the park also. Plus, I only burn wood that is a couple of years old (the borer can't live long on dead wood), and the wood I have is apple, oak, and sycamore.....not ash. Of course, the Park can't just say it is OK for me because I live close......I can't prove where my wood came from. And I seriously wonder exactly where the "certified" wood comes from that the buy for purchase ......I betcha it is further away than 20 miles.
The Park does allow cutting dead and down limbs in certain sections of the Park with with hand saws for campground firewood only. I take along my battery powered reciprocating saw, and park along the road or at an overlook, and there is still plenty of wood within a short walk. 1 time a Ranger stopped and asked to see what I was using to cut with, but didn't give me any grief about the battery powered saw.
I have noticed that many campgrounds have people that have firewood for sale on the way to the public campgrounds.....those vendors might be an option if not camping in state or federal campgrounds where the outside firewood is forbidden.
Sigh.....even with my surplus of wood at home, I abide by the rules and buy wood at the state or federal campgrounds. I got a couple of years worth of wood for my home fire-pit.