Here is another toy in Engino's series of toys that teach mechanical principles. These are the folks that created the set on cams and cranks. The Engino toy system is a construction toy made up of of multi-faceted rods and connectors that can be connected on up to 6 sides at the same time. The design allows dense or open construction methods, simple or complex models, and the need for a smaller number of different components than other three dimensional building systems. Linkages seem like an idea application.
From the toy description:
Engino Mechanical Science: Linkages. This Engino set introduces young engineers and physicists the concept of linking levers to connect to moving parts for complex motion. Build 6 working models including a mechanical, extendable arm, a lifting platform, a pantograph, a folding ladder, a parallel weighing scale and a moving toy. A 40 page activity book is included with innovative experiments and detailed explanations of various technical and scientific principles and how they are applied.
Here is where you can get the linkages experiment set.