It is not physical but CBiS Education have release a free robot arm simulator for Scratch.
Downloadable from their site http://www.cbinfosystems.com/cardboard2code_module2.aspx - it includes a Scratch project, guidance on Scratch along with an exercises in using the robot arm simulation and an exercise with teacher's guidance.
Left my son with it, asked him if he could make it do something if a new sprite is added and the gripper touched it (similar to the exercise in the notes). He went on to produce a sprite that when it is touched by the gripper, went on to change colour a few times. I could see this being potentially used in Coding Clubs within schools.
CBiS produce a physical version of this, details are available at http://www.cbinfosystems.com/cardboard2code_module3.aspx
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