At least when I was actively looking at hardware (2011-2018), 4 socket Xeon was available off the shelf, but at quite the premium over 2 socket Xeon. If your load scaled horizontally, it still made sense to get a 2P Xeon over 2x 1P Xeon, but 2x 2P Xeon was way more cost efficient than a 4P Xeon. 8P or 16P seemed to exist, but maybe only in catalogs.

I'm not really in the market anymore, but Epyc looks like 1P is going to solve a lot of needs, and 2P will be available at a reasonable premium, but 4P will probably be out of reach.