As a follow up, the Airport ended up being the way to go.
I tried using CVS, which had a location around a 10 minute walk away from the convention center. Their website wanted a SIN or US Drivers license. Not being American, I had neither. I tried calling their customer service line, which was equally unhelpful. I walked to the CVS directly, said "your site says you have slots available, and I'm happy to pay for the test", but they still couldn't do anything.
There were other services in the area, but most of them either weren't available on weekends, were too far afield to get to (I wasn't looking to take an hour long road trip with one of our already tired drivers or on mass transit/an Uber), or otherwise not workable (too distant mixed with highly limited hours, etc).
In the end, the Airport was the way to go. Not surprisingly, they're obviously focused on assisting travelers of all sorts, including international ones.
Hopefully next year we're at a place where testing isn't necessary, or if it is, the infrastructure exists to make it smoother/more cost effective. But I thought I'd mention it on the off chance someone looking to travel for a conference or something was looking for insight on the matter. Perhaps just limited to my personal experience with one con in one state during these shenanigans, but I felt it was worth sharing all the same.