Newton Messagepad 120

It took over a year to upgrade the original Newton, mainly because the Newton team worked over 6 years and the bad press left the morale low. People say the Newton didn't succeed because it was "way ahead of its time."

"On August 2nd, 1993 Apple released the first PDA (Newton MessagePad). Although highly anticipated by the press, the Newton's handwriting recognition fails to deliver the announced reliabilty, breaking the neck of the Newton PDA project already at its introduction. Apple dropped the Newton devision only four years after the introduction of the first Newton MessagePad." - apple museum

Since this is an obsolete product, the best place to find one would be eBay.