Does anyone know of an authoritative source for the actual focal lengths (not 35mm equivalent) for DJI camera / lens setups? I'm compiling a list of drones for a photogrammetry projects and I need the actual focal lengths of the lenses; the 35mm equivalent numbers won't work in some of the ground resolution formulas. Any assistance would be appreciated. Thanks.

You can find them in the specs on the DJI page.
For most drones at least.

Check this site :

https://www.dji.com/nl/products/ ... ndsite&from=nav

You can choose most drones (consumer versions at least)

All listed on the specs section of each drone on dji.com