Since the Minecraft Overviewer still has yet to provide support for version 1.13, I've decided to migrate us over to a new map generator with a product called Mapcrafter. This generates something very familiar to what we had set up before, but has a bit different lighting.
You can access the map in the same location at mcmap.procrastinationhub.net.
Thanks to Jmasie for the recommendation.
The map refreshes every day at 5 AM MST/MDT.