Adding to the background website lists and to let you know that I made a drive that contains overlays cut out from the backgrounds in the portal --all those unusable backgrounds that have furniture in the way where characters would stand etc. – It’s a pretty extensive drive but if you see a background that needs overlays, I’ll happily do it and add them to the drive for everyone’s use. I also don’t require credit for use of them. Episode Overlays, Free Use
but, on to websites: freepik.com is a good place to find free and premium (paid for) backgrounds. There’s a daily download limit ( I think it’s 10 images per day for free accounts and unlimited for the premium subscription.
episodelife.com is also good, just be sure to read the written stuff below the images to see if the creator requires credits and how they want that done. 
Also, a tip, if you do use images from the threads here, Save them like this " INT. CAFE - DAY @ colecatalyst " <<< this will keep you from forgetting who made what as lists and saved files can get misplaced or accidentally deleted etc.
Threads to check out:
💗 Marysol.Episode's Background Thread 💗
🌷 FlowerGriefer's Backgrounds 🌷
**OFFICIAL** Overlay Sharing Thread
Official Background Sharing Thread
^^^be sure to read through the comments too because sometimes artists forget to add their credit info to posts but will comment how to credit them when someone asks. Also, do not share any art without expressed permission from the creator – doing so is a good way to lose access, which no one wants.
Good luck, hon.