Not exactly portable, but Wersi make the Giga Piano with 88 Notes and Hammer action keyboard complete with the OAS Expander all in one Piano type cabinet.
The Piano Sound I believe is “The Grand” Giga Sample from Steinberg, link below, unfortunately it is still in German at the moment, but you should get the idea and Babel Fish will do a reasonable translation. I have also included the American site, which unfortunately always seems to be a long way behind the rest of the World.
(Don’t Wersi USA realise what a big market that they have access to)
http://www.wersi.net/html/gigapiano.html http://www.wersimusic.com/pianos1.htm

Bill