The Civil Air Patrol (US Air Force affiliate) has many STEM lessons and kits available to educators for a one-time fee. The kits include robotics, microcontrollers, telescoopes, flight simulators and others.

This website, maintained by elementary STEM consultant Bob Claymier, contains:
1) A list of over 40 STEM resources for grades K-6 ( construction materials, books, curriculum, websites) related to elementary STEM.

2) a list of over 40 robotics and coding resources for grades K-6

3) A free set of standards-based science lessons for grades K-6, all with an engineering component

4) A free monthly elementary STEM newsletter (current and archived editions) that contain information on resources, events, and articles pertaining to elementary STEM.