I don't see any that the mfr. specifically says is good for a washing machine but chronomite and eemax have "instant" hots sized for a variety of applications from dishwashers to whole house units.
Having said that, I would never put one in my house. When I have clients request them I always warn them that I've never seen one locally last two years, most die in a year.
The gas models seem to have better setups with their heat exchangers.