I’ve edited a couple of documentaries that lack usable interview video and b-roll, and I would encourage you to investigate archival and stock footage libraries for video and photos that illuminate the sound bites you have. It helps to have at least a rough script in place, then you can set about finding footage that matches your content. If you are writing as you edit, consider how you will visually match the content as you go to help you make choices that will work.
If you have the means and budget to do so, you can also shoot new footage to accompany your script. You can see this technique in countless documentaries and it can be either evocative (as Andrew suggested) or specific, re-creating events using actors and/or locations whose identifying characteristics remain hidden. You can use filters and looks to age footage to match different eras. I recently noticed this technique used effectively in The Andy Warhol Diaries on Netflix, in which even the audio soundbites are created using AI-assisted voice simulation.
Many if not most stock libraries include 4K clips which allow you to add zooms and pans if you are finishing in HD.
Make sure you check the terms of the licenses whether you are paying or not. Different licenses cover different uses and intended distribution.
Sources of footage I can recommend include:
archive.org – a rich and free source of historical archival footage stretching back to the dawn of filmmaking.
commons.wikimedia.org – a wide variety of free photos and footage of all kinds. Each download has different terms of use, many if not most require attribution.
wpafilmlibrary.com – a relatively expensive source of footage of significant historical events.
criticalpast.com – similar to WPA
storyblocks.com – a large library of mediocre to spectacular footage that gives unlimited downloads for a flat fee depending on your use. You will find some of the same clips that more expensive libraries have here. You will learn how to search more effectively for what you want as you go through thousands of search results.
shutterstock.com – a low-to-medium-priced library with fewer mediocre clips and a better search engine than Storyblocks. Terms and prices for the same clips found in other libraries may differ.
pond5.com – similar to Shutterstock with many of the same clips. Terms and prices for the same clips found in other libraries may differ.
envato.elements.com – similar to Storyblocks and even less expensive but with a more limited selection. Clips must be registered to individual projects.
stock.adobe.com – I haven’t used them yet. Pay per clip, medium-priced for clip-based services.
There are many more libraries but I can vouch for the above.
Good luck with your project!