Interestingly enough TTL monitors are still manufactured.

http://www.miraclebusiness.com/mt117.htm

Though they don't support the correct sync rates.

Thinking about it I think an EGA monitor will be you best bet. Though I don't think it will work out of the box. The built in controls might get you close enough to work at .4KHz out.

I would suggest taking a look at the service manual for some EGA monitors. They should mention the tolerance for the input signal and maybe some clue as how to change the input timing.

Another thought. A quick google shows there are a few VGA monitors that can sync that low. You might be able to cobble together a Digital Analog Converter out of a hand full of resistors. Then you could use a VGA monitor. http://www.play-hookey.com/analog/d2a_converter.html