I saw a picture of one in a book whose name I can't recall, but there is
a longish scene in an animated movie (Nadia and the Blue Water or Nadia
and the Secret of Blue Water or Nadia something something Blue Water) in
which one of the protagonists rides a monocycle. I think that this video
will most likely be found in the Japanese animation or animation section
of any reasonably large video rental place. I've heard that lots of
people hated the dubbing, so it might not be worthwhile just for that one
chase scene (which also involves an amphibious/air capable tank.)
Since I'm only being semi-serious anyway, I'ld recommend that you go with
someone else's recommendation.
Ken