How can I share reusable blocks from the main site to all subfolder sites?

Background:
I am in the planning stages of a WordPress multisite where I plan to write a custom theme from scratch and use the block editor for page layouts. The page is for an organization that has multiple locations, one main national site and a subfolder site for each location. This is needed to restrict editors to their own location. The page will rely heavily on reusable blocks and block patterns. Block patterns I will code into the theme.