Not exactly a zoom, but Leica did a 28-35-50mm all-in-one lens: http://www.reddotcameras.co.uk/m-lenses/8281-leica-tri-elmar-28-35-50mm-f4-asph-m.html
There was a wide version as well.
And they would be usable as zooms on a dcamera with shorter registration or the Ricoh...





