You can still buy new MS-DOS computers, for use with legacy equipment and software, like industrial machinery. The most powerful CPU this company is offering is a Pentium D from 2006:

https://nixsys.com/legacy-computers/ms-dos-computers

For an extra $95, they'll pre-install MS-DOS 6.22 for you, but it will of course only use 64 MB of the 1 GB RAM the machine comes with. That's a luxurious amount already. I've never used more than 48 MB with MS DOS and it was already more than plenty.

Motherboards for the LGA 775 socket were among the last to support ISA cards, which are why companies buy these new legacy computers in the first place. There's machinery out there worth millions and running entire factories, complex scientific instruments or medical equipment that requires interfacing with ISA cards. I've seen this myself and fixed a few of these systems. It's fun to take a machine off the factory floor that has been quietly doing its job for many decades. You wouldn't believe how much of the world is running on truly ancient hardware.

While it would be theoretically possible to e.g. create a new hardware interface and compatible software, this would not only be prohibitively expensive on its own, but require costly and lengthy certification on top, which just isn't feasible most of the time. That's where PCs like these come in. They may seem outrageously expensive given the ancient hardware they consist of, but compared to the equipment they'll be used with, they might as well be free - and on top of that, they come with a warranty, support hotline, etc. - unlike cobbling something together from old parts found on ebay.