https://drive.google.com/file/d/1KBEAiZCGVJU6zcB6wufO7Ff_JPvREZAc/view?usp=drive_link
I took a little time out of my weekend to make these, feel free to download. I just used an image extractor website to save all 800 or so official borders from this website in one go: https://www.vgmuseum.com/features/sgb/
Then I ran a plug-in on GIMP to both crop and convert the images to the correct BMP format in batches, and there ya go. Obviously the cropping doesn't work great for some of them, a lot of logos and such get cut off due to the shorter height of the DS console's resolution, but there's a lot of great options here! Also, I didn't rename the image files, so some of them might be difficult to identify without a thumbnail or preview.
I know GameYob runs official SGB borders with their respective games automatically if you've enabled them, but this way you can play a game with a completely different game's official border! (Like play Pokémon Red with Pokémon Blue's border... ooo, so naughty!)