Snap-in educational and fully functional circuits: https://www.elenco.com/snap-circuits-2/
Science & crafts toys: https://www.johncoproductions.com/collections/4m
Green & renewable energy toys: https://www.johncoproductions.com/collections/green-science
(Edit: For the second two links, apparently that is a non-US vendor. Sorry about that. But those toys are also commonly available in the US, at toy stores and often, museum gift stores)