Check in EBAY. These are great type of fasteners needed to be used to keep things closed and secured but also needed to be accessed without tools such as panels or light fixtures. Great for outdoor use where rust can be a problem, I used them on some panels under some outdoor light fixture sconces, they had an open bottom and I made some solid panels to close off the bottoms to keep out bugs, wasps and dirt daubers from building nests in them. I drilled and tapped some threads into the frame of the light fixture and I used these thumb screws to secure the panels I made. I also painted the heads of the screws to match the color of the light fixture. They worked very well!

Sad part about my local ACE Store is they dropping all Black Screw.
At least they well still have the Stainless Steal Screws and Nuts.

maxfly
https://www.fastenal.com/products/details/0145215
just make sure you have the length correct. i would grab some m4 screws of the same type. just to be sure you have them if you need them.

Black Oxide Finish Stainless Steel Machine