I've never seen anything that small in the US. It'll probably have to
be custom made or you'll have to do it your self.
I saw lots in Japan when I was there, including a complete bathroom
about 2.5 times the size of of a 747 toilet. It was made by Hitachi,
all one unit, looks like they just dropped them in place, wired them
in, hooked up the plumbing, done.
Richard