I don't really want to enter into a dialogue on this, but try stretching your imagination to its limit and see if you can think of any reasons why your suggestion might not be possible and therefor quite offensive.
I've had to use a bucket and toilet plunger for my laundry all these years. I always wanted a washing machine (sigh), so my hackles rise when I hear a man (you won't hear a woman saying it too often) tell me I should just do it the old-fashioned way!
I don't know of any, but a few suggestions. You could get a regular AC washer, install an inverter on your boat. Check with Hoover, their all plastic washers. Check Recreational Vehicle suppliers.
I remember seeing one on a UK boat many years ago, but don't know if it was 12V or not. It was small, didn't have much in the way of features - you filled with a hose, turned it on to agitate, turned the dial or pushed a button (I forget which) to spin. It was quite small, low profile. I assume it was made for the recreational vehicle/camping market. Good luck!
Good suggestions, but I don't think that inverters are such a bad idea. Nowadays most inverters are quite efficient, you're only losing about 1 AH DC in running it. Of course, you need to turn it off when it's not needed, but that's not such a big deal. The advantage is that you aren't paying the great premium for special 12V engines. Or, as in the case of our refrigerator, which is a 12V DC, it has its own built-in inverter, the compressor is actually an AC motor. It would have been cheaper, and easier, in the long run, to have put in an AC compressor and a sturdy house inverter.
So, if your batteries are not sufficient to run a motor through the inverter, the chances are pretty good that they won't be able to run a DC version of the motor you want.
Anybody who is planning on running washing machine is already into a different style of cruising, and I would expect them to have sufficient battery banks to support the power needs of a liveaboard cruiser.
I'm fairly certain there isn't a 12volt washing machine on the market, but JeanneP's comments re inverter operation are perfectly valid. If you want a washer for a boat, and have room for it, then I'm sure you have space for a big battery bank.
The washer most mentioned in liveaboard cruising notes is the "Splendide", made in Italy. It's very compact (24" wide) and only needs about 1300watts - so it would run quite easily off an inverter. And it's actually a washer/drier. I haven't a clue whether you can buy one in UK (assuming you're in UK), but West Marine sell it. See www.splendide.com for pics and lots of info.
Of course, like lots of specialist equipment, the Splendide is quite expensive. If you have space, might be worth getting a regular domestic "compact" washer, but this would undoubtedly need a beefier inverter.