Leblanc makes one. They start at just under $6K. They also make a D clarinet. I love the D clarinets.

OK, I know the D can be used in Strauss' "Til Eulenspiegel"(sp?), but what is written where for Ab clarinet?

They're mainly used in military bands in Europe and Australia, though parts are rarely found. I suppose the place that you might see them most often would be in clarinet choirs.

Mostly you will find music for it in the Clarinet Choir music. Although, it is still used occaisionally in the recording studios for movie music and game music (Xbox,etc).