In working with the KidWind nonprofit organization, we developed kits that are as inexpensive as possible. The kits contain the most popular configurations of the parts needed to teach the concepts of renewable energy. In many cases, we do sell parts individually and list these at:
https://www.vernier.com/products/kidwind/wind-energy/

However, it is not possible for us to break these kits down into their smaller components. Our handling cost to sell (for example) just one gear is quite high. Instead, we created an inexpensive kit KidWind Gear Set (KW-GEAR) that includes one of each gear.

We have posted designs for several items that can be 3D printed on our Thingiverse page at:
https://www.thingiverse.com/vernier/collections/energy-science