Lobster can be fished year round, but the season usually shuts down around December since the lobsters are migrating out to deeper/colder water. That said, the fall is said to be the peak hardshell season, since all of the shedders now have new hard shells and start to head back out to the deep water. A lot get trapped on their way out.
Anyhow, plenty of pounds close in the late fall since they aren't getting the traffic to stay open, but you can expect lobster anywhere that it's normally served as long as the place itself is open. I can't speak to other parts of Maine, but if you're in the Portland area, it won't be a challenge to find lobster in mid-October.