This is cool. The Franchise Tax Board has an online feature call the Entity Status Letter which allows you to quickly find whether an NPO is exempt with the state of California.
You can go to the Self Serve Entity Status Letter – Entity Search page. If the link breaks, just search “entity status letter” at the FTB website.
This will also work for a for-profit business.
When you find the organization, you can print a PDF file that says the organization is in good standing with the FTB and that they are exempt under 23701d.