I have to say I agree with Larry - why would you want to cover the stucco? I LOVE stucco. but perhaps you have a good reason.
anyway - about the water heater -- i don't know of a source, but if I understand what you are looking for, they are widely used in Hawaii, where I used to live. These heaters do not have a holding tank, but just heat the water as you use it (as the water goes through the unit). I'm going to use one in my house that I'm building in Oregon -- they're great!!