I reached out to John at The Boardsmith and he does indeed take custom orders. He was super helpful and good with communication, but unfortunately is running about six weeks lead time on custom orders right now which was longer than I wanted to wait if I could avoid it.
I found a woodworking outfit here in Kentucky, LIMBA Woodcraft (https://www.furniturehomecraft.com/collections/end-grain) that makes some beautiful looking boards and also take custom orders. They do ship nationwide, and are making me a 20” x 20” x 3” end grain walnut board that will ship next week. Also good communication, and prices are comparable to Boardsmith, maybe moderately less expensive.
I’ll post some pics when I receive it.