One thing that I do when I’m writing about current events is very carefully examine Wikimedia Commons, where photos for Wikipedia among other things are stored. Almost all the photos on Wikimedia Commons are available for free.
I also pay $25 a month Adobe stock, which gives me 10 images for the month. I can’t afford to use it every day, but when I do use it the abundance of available images is just amazing.
For your particular militia story, remember that photos that people post to public Facebook pages are fair game. You don’t need permission to use them.
So if you were able to find militia groups with a Facebook presence, you could search for a photo that way. Just credit the photo with a link to the page or post where it came from.
Oh, and YouTube videos are also fair game if you want to make a screenshot.